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![Waiman Long](/assets/img/avatar_default.png)
Make some miscellaneous fixes to the first paragraph of "ECC memory": - Change the incorrect "74 bits" to "72 bits". - Change "mentioned on" to "mentioned in". - Remove the extra "extra". - Rephrase some sentences as suggested by Matthew Wilcox. Signed-off-by: Waiman Long <longman@redhat.com> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Link: https://lore.kernel.org/r/20200506162217.16633-1-longman@redhat.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1219 lines
42 KiB
ReStructuredText
1219 lines
42 KiB
ReStructuredText
.. include:: <isonum.txt>
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============================================
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Reliability, Availability and Serviceability
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============================================
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RAS concepts
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************
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Reliability, Availability and Serviceability (RAS) is a concept used on
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servers meant to measure their robustness.
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Reliability
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is the probability that a system will produce correct outputs.
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* Generally measured as Mean Time Between Failures (MTBF)
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* Enhanced by features that help to avoid, detect and repair hardware faults
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Availability
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is the probability that a system is operational at a given time
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* Generally measured as a percentage of downtime per a period of time
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* Often uses mechanisms to detect and correct hardware faults in
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runtime;
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Serviceability (or maintainability)
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is the simplicity and speed with which a system can be repaired or
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maintained
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* Generally measured on Mean Time Between Repair (MTBR)
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Improving RAS
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-------------
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In order to reduce systems downtime, a system should be capable of detecting
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hardware errors, and, when possible correcting them in runtime. It should
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also provide mechanisms to detect hardware degradation, in order to warn
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the system administrator to take the action of replacing a component before
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it causes data loss or system downtime.
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Among the monitoring measures, the most usual ones include:
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* CPU – detect errors at instruction execution and at L1/L2/L3 caches;
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* Memory – add error correction logic (ECC) to detect and correct errors;
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* I/O – add CRC checksums for transferred data;
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* Storage – RAID, journal file systems, checksums,
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Self-Monitoring, Analysis and Reporting Technology (SMART).
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By monitoring the number of occurrences of error detections, it is possible
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to identify if the probability of hardware errors is increasing, and, on such
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case, do a preventive maintenance to replace a degraded component while
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those errors are correctable.
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Types of errors
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---------------
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Most mechanisms used on modern systems use technologies like Hamming
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Codes that allow error correction when the number of errors on a bit packet
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is below a threshold. If the number of errors is above, those mechanisms
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can indicate with a high degree of confidence that an error happened, but
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they can't correct.
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Also, sometimes an error occur on a component that it is not used. For
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example, a part of the memory that it is not currently allocated.
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That defines some categories of errors:
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* **Correctable Error (CE)** - the error detection mechanism detected and
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corrected the error. Such errors are usually not fatal, although some
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Kernel mechanisms allow the system administrator to consider them as fatal.
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* **Uncorrected Error (UE)** - the amount of errors happened above the error
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correction threshold, and the system was unable to auto-correct.
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* **Fatal Error** - when an UE error happens on a critical component of the
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system (for example, a piece of the Kernel got corrupted by an UE), the
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only reliable way to avoid data corruption is to hang or reboot the machine.
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* **Non-fatal Error** - when an UE error happens on an unused component,
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like a CPU in power down state or an unused memory bank, the system may
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still run, eventually replacing the affected hardware by a hot spare,
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if available.
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Also, when an error happens on a userspace process, it is also possible to
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kill such process and let userspace restart it.
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The mechanism for handling non-fatal errors is usually complex and may
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require the help of some userspace application, in order to apply the
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policy desired by the system administrator.
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Identifying a bad hardware component
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------------------------------------
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Just detecting a hardware flaw is usually not enough, as the system needs
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to pinpoint to the minimal replaceable unit (MRU) that should be exchanged
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to make the hardware reliable again.
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So, it requires not only error logging facilities, but also mechanisms that
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will translate the error message to the silkscreen or component label for
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the MRU.
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Typically, it is very complex for memory, as modern CPUs interlace memory
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from different memory modules, in order to provide a better performance. The
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DMI BIOS usually have a list of memory module labels, with can be obtained
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using the ``dmidecode`` tool. For example, on a desktop machine, it shows::
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Memory Device
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Total Width: 64 bits
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Data Width: 64 bits
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Size: 16384 MB
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Form Factor: SODIMM
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Set: None
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Locator: ChannelA-DIMM0
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Bank Locator: BANK 0
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Type: DDR4
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Type Detail: Synchronous
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Speed: 2133 MHz
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Rank: 2
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Configured Clock Speed: 2133 MHz
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On the above example, a DDR4 SO-DIMM memory module is located at the
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system's memory labeled as "BANK 0", as given by the *bank locator* field.
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Please notice that, on such system, the *total width* is equal to the
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*data width*. It means that such memory module doesn't have error
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detection/correction mechanisms.
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Unfortunately, not all systems use the same field to specify the memory
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bank. On this example, from an older server, ``dmidecode`` shows::
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Memory Device
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Array Handle: 0x1000
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Error Information Handle: Not Provided
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Total Width: 72 bits
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Data Width: 64 bits
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Size: 8192 MB
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Form Factor: DIMM
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Set: 1
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Locator: DIMM_A1
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Bank Locator: Not Specified
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Type: DDR3
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Type Detail: Synchronous Registered (Buffered)
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Speed: 1600 MHz
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Rank: 2
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Configured Clock Speed: 1600 MHz
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There, the DDR3 RDIMM memory module is located at the system's memory labeled
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as "DIMM_A1", as given by the *locator* field. Please notice that this
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memory module has 64 bits of *data width* and 72 bits of *total width*. So,
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it has 8 extra bits to be used by error detection and correction mechanisms.
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Such kind of memory is called Error-correcting code memory (ECC memory).
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To make things even worse, it is not uncommon that systems with different
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labels on their system's board to use exactly the same BIOS, meaning that
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the labels provided by the BIOS won't match the real ones.
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ECC memory
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----------
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As mentioned in the previous section, ECC memory has extra bits to be
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used for error correction. In the above example, a memory module has
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64 bits of *data width*, and 72 bits of *total width*. The extra 8
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bits which are used for the error detection and correction mechanisms
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are referred to as the *syndrome*\ [#f1]_\ [#f2]_.
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So, when the cpu requests the memory controller to write a word with
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*data width*, the memory controller calculates the *syndrome* in real time,
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using Hamming code, or some other error correction code, like SECDED+,
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producing a code with *total width* size. Such code is then written
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on the memory modules.
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At read, the *total width* bits code is converted back, using the same
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ECC code used on write, producing a word with *data width* and a *syndrome*.
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The word with *data width* is sent to the CPU, even when errors happen.
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The memory controller also looks at the *syndrome* in order to check if
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there was an error, and if the ECC code was able to fix such error.
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If the error was corrected, a Corrected Error (CE) happened. If not, an
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Uncorrected Error (UE) happened.
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The information about the CE/UE errors is stored on some special registers
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at the memory controller and can be accessed by reading such registers,
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either by BIOS, by some special CPUs or by Linux EDAC driver. On x86 64
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bit CPUs, such errors can also be retrieved via the Machine Check
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Architecture (MCA)\ [#f3]_.
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.. [#f1] Please notice that several memory controllers allow operation on a
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mode called "Lock-Step", where it groups two memory modules together,
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doing 128-bit reads/writes. That gives 16 bits for error correction, with
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significantly improves the error correction mechanism, at the expense
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that, when an error happens, there's no way to know what memory module is
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to blame. So, it has to blame both memory modules.
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.. [#f2] Some memory controllers also allow using memory in mirror mode.
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On such mode, the same data is written to two memory modules. At read,
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the system checks both memory modules, in order to check if both provide
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identical data. On such configuration, when an error happens, there's no
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way to know what memory module is to blame. So, it has to blame both
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memory modules (or 4 memory modules, if the system is also on Lock-step
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mode).
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.. [#f3] For more details about the Machine Check Architecture (MCA),
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please read Documentation/x86/x86_64/machinecheck.rst at the Kernel tree.
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EDAC - Error Detection And Correction
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*************************************
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.. note::
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"bluesmoke" was the name for this device driver subsystem when it
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was "out-of-tree" and maintained at http://bluesmoke.sourceforge.net.
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That site is mostly archaic now and can be used only for historical
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purposes.
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When the subsystem was pushed upstream for the first time, on
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Kernel 2.6.16, it was renamed to ``EDAC``.
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Purpose
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-------
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The ``edac`` kernel module's goal is to detect and report hardware errors
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that occur within the computer system running under linux.
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Memory
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------
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Memory Correctable Errors (CE) and Uncorrectable Errors (UE) are the
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primary errors being harvested. These types of errors are harvested by
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the ``edac_mc`` device.
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Detecting CE events, then harvesting those events and reporting them,
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**can** but must not necessarily be a predictor of future UE events. With
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CE events only, the system can and will continue to operate as no data
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has been damaged yet.
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However, preventive maintenance and proactive part replacement of memory
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modules exhibiting CEs can reduce the likelihood of the dreaded UE events
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and system panics.
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Other hardware elements
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-----------------------
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A new feature for EDAC, the ``edac_device`` class of device, was added in
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the 2.6.23 version of the kernel.
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This new device type allows for non-memory type of ECC hardware detectors
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to have their states harvested and presented to userspace via the sysfs
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interface.
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Some architectures have ECC detectors for L1, L2 and L3 caches,
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along with DMA engines, fabric switches, main data path switches,
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interconnections, and various other hardware data paths. If the hardware
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reports it, then a edac_device device probably can be constructed to
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harvest and present that to userspace.
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PCI bus scanning
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----------------
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In addition, PCI devices are scanned for PCI Bus Parity and SERR Errors
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in order to determine if errors are occurring during data transfers.
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The presence of PCI Parity errors must be examined with a grain of salt.
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There are several add-in adapters that do **not** follow the PCI specification
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with regards to Parity generation and reporting. The specification says
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the vendor should tie the parity status bits to 0 if they do not intend
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to generate parity. Some vendors do not do this, and thus the parity bit
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can "float" giving false positives.
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There is a PCI device attribute located in sysfs that is checked by
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the EDAC PCI scanning code. If that attribute is set, PCI parity/error
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scanning is skipped for that device. The attribute is::
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broken_parity_status
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and is located in ``/sys/devices/pci<XXX>/0000:XX:YY.Z`` directories for
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PCI devices.
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Versioning
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----------
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EDAC is composed of a "core" module (``edac_core.ko``) and several Memory
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Controller (MC) driver modules. On a given system, the CORE is loaded
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and one MC driver will be loaded. Both the CORE and the MC driver (or
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``edac_device`` driver) have individual versions that reflect current
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release level of their respective modules.
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Thus, to "report" on what version a system is running, one must report
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both the CORE's and the MC driver's versions.
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Loading
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-------
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If ``edac`` was statically linked with the kernel then no loading
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is necessary. If ``edac`` was built as modules then simply modprobe
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the ``edac`` pieces that you need. You should be able to modprobe
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hardware-specific modules and have the dependencies load the necessary
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core modules.
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Example::
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$ modprobe amd76x_edac
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loads both the ``amd76x_edac.ko`` memory controller module and the
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``edac_mc.ko`` core module.
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Sysfs interface
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---------------
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EDAC presents a ``sysfs`` interface for control and reporting purposes. It
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lives in the /sys/devices/system/edac directory.
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Within this directory there currently reside 2 components:
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======= ==============================
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mc memory controller(s) system
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pci PCI control and status system
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======= ==============================
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Memory Controller (mc) Model
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----------------------------
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Each ``mc`` device controls a set of memory modules [#f4]_. These modules
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are laid out in a Chip-Select Row (``csrowX``) and Channel table (``chX``).
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There can be multiple csrows and multiple channels.
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.. [#f4] Nowadays, the term DIMM (Dual In-line Memory Module) is widely
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used to refer to a memory module, although there are other memory
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packaging alternatives, like SO-DIMM, SIMM, etc. The UEFI
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specification (Version 2.7) defines a memory module in the Common
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Platform Error Record (CPER) section to be an SMBIOS Memory Device
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(Type 17). Along this document, and inside the EDAC subsystem, the term
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"dimm" is used for all memory modules, even when they use a
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different kind of packaging.
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Memory controllers allow for several csrows, with 8 csrows being a
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typical value. Yet, the actual number of csrows depends on the layout of
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a given motherboard, memory controller and memory module characteristics.
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Dual channels allow for dual data length (e. g. 128 bits, on 64 bit systems)
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data transfers to/from the CPU from/to memory. Some newer chipsets allow
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for more than 2 channels, like Fully Buffered DIMMs (FB-DIMMs) memory
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controllers. The following example will assume 2 channels:
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+------------+-----------------------+
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| CS Rows | Channels |
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+------------+-----------+-----------+
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| | ``ch0`` | ``ch1`` |
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+============+===========+===========+
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| |**DIMM_A0**|**DIMM_B0**|
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+------------+-----------+-----------+
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| ``csrow0`` | rank0 | rank0 |
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+------------+-----------+-----------+
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| ``csrow1`` | rank1 | rank1 |
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+------------+-----------+-----------+
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| |**DIMM_A1**|**DIMM_B1**|
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+------------+-----------+-----------+
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| ``csrow2`` | rank0 | rank0 |
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+------------+-----------+-----------+
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| ``csrow3`` | rank1 | rank1 |
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+------------+-----------+-----------+
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In the above example, there are 4 physical slots on the motherboard
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for memory DIMMs:
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||
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+---------+---------+
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| DIMM_A0 | DIMM_B0 |
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+---------+---------+
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| DIMM_A1 | DIMM_B1 |
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+---------+---------+
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Labels for these slots are usually silk-screened on the motherboard.
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Slots labeled ``A`` are channel 0 in this example. Slots labeled ``B`` are
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channel 1. Notice that there are two csrows possible on a physical DIMM.
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These csrows are allocated their csrow assignment based on the slot into
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which the memory DIMM is placed. Thus, when 1 DIMM is placed in each
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Channel, the csrows cross both DIMMs.
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||
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Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
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||
In the example above 2 dual ranked DIMMs are similarly placed. Thus,
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both csrow0 and csrow1 are populated. On the other hand, when 2 single
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ranked DIMMs are placed in slots DIMM_A0 and DIMM_B0, then they will
|
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have just one csrow (csrow0) and csrow1 will be empty. The pattern
|
||
repeats itself for csrow2 and csrow3. Also note that some memory
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controllers don't have any logic to identify the memory module, see
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``rankX`` directories below.
|
||
|
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The representation of the above is reflected in the directory
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||
tree in EDAC's sysfs interface. Starting in directory
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``/sys/devices/system/edac/mc``, each memory controller will be
|
||
represented by its own ``mcX`` directory, where ``X`` is the
|
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index of the MC::
|
||
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||
..../edac/mc/
|
||
|
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||
|->mc0
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|->mc1
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||
|->mc2
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||
....
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||
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Under each ``mcX`` directory each ``csrowX`` is again represented by a
|
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``csrowX``, where ``X`` is the csrow index::
|
||
|
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.../mc/mc0/
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||
|
|
||
|->csrow0
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||
|->csrow2
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||
|->csrow3
|
||
....
|
||
|
||
Notice that there is no csrow1, which indicates that csrow0 is composed
|
||
of a single ranked DIMMs. This should also apply in both Channels, in
|
||
order to have dual-channel mode be operational. Since both csrow2 and
|
||
csrow3 are populated, this indicates a dual ranked set of DIMMs for
|
||
channels 0 and 1.
|
||
|
||
Within each of the ``mcX`` and ``csrowX`` directories are several EDAC
|
||
control and attribute files.
|
||
|
||
``mcX`` directories
|
||
-------------------
|
||
|
||
In ``mcX`` directories are EDAC control and attribute files for
|
||
this ``X`` instance of the memory controllers.
|
||
|
||
For a description of the sysfs API, please see:
|
||
|
||
Documentation/ABI/testing/sysfs-devices-edac
|
||
|
||
|
||
``dimmX`` or ``rankX`` directories
|
||
----------------------------------
|
||
|
||
The recommended way to use the EDAC subsystem is to look at the information
|
||
provided by the ``dimmX`` or ``rankX`` directories [#f5]_.
|
||
|
||
A typical EDAC system has the following structure under
|
||
``/sys/devices/system/edac/``\ [#f6]_::
|
||
|
||
/sys/devices/system/edac/
|
||
├── mc
|
||
│ ├── mc0
|
||
│ │ ├── ce_count
|
||
│ │ ├── ce_noinfo_count
|
||
│ │ ├── dimm0
|
||
│ │ │ ├── dimm_ce_count
|
||
│ │ │ ├── dimm_dev_type
|
||
│ │ │ ├── dimm_edac_mode
|
||
│ │ │ ├── dimm_label
|
||
│ │ │ ├── dimm_location
|
||
│ │ │ ├── dimm_mem_type
|
||
│ │ │ ├── dimm_ue_count
|
||
│ │ │ ├── size
|
||
│ │ │ └── uevent
|
||
│ │ ├── max_location
|
||
│ │ ├── mc_name
|
||
│ │ ├── reset_counters
|
||
│ │ ├── seconds_since_reset
|
||
│ │ ├── size_mb
|
||
│ │ ├── ue_count
|
||
│ │ ├── ue_noinfo_count
|
||
│ │ └── uevent
|
||
│ ├── mc1
|
||
│ │ ├── ce_count
|
||
│ │ ├── ce_noinfo_count
|
||
│ │ ├── dimm0
|
||
│ │ │ ├── dimm_ce_count
|
||
│ │ │ ├── dimm_dev_type
|
||
│ │ │ ├── dimm_edac_mode
|
||
│ │ │ ├── dimm_label
|
||
│ │ │ ├── dimm_location
|
||
│ │ │ ├── dimm_mem_type
|
||
│ │ │ ├── dimm_ue_count
|
||
│ │ │ ├── size
|
||
│ │ │ └── uevent
|
||
│ │ ├── max_location
|
||
│ │ ├── mc_name
|
||
│ │ ├── reset_counters
|
||
│ │ ├── seconds_since_reset
|
||
│ │ ├── size_mb
|
||
│ │ ├── ue_count
|
||
│ │ ├── ue_noinfo_count
|
||
│ │ └── uevent
|
||
│ └── uevent
|
||
└── uevent
|
||
|
||
In the ``dimmX`` directories are EDAC control and attribute files for
|
||
this ``X`` memory module:
|
||
|
||
- ``size`` - Total memory managed by this csrow attribute file
|
||
|
||
This attribute file displays, in count of megabytes, the memory
|
||
that this csrow contains.
|
||
|
||
- ``dimm_ue_count`` - Uncorrectable Errors count attribute file
|
||
|
||
This attribute file displays the total count of uncorrectable
|
||
errors that have occurred on this DIMM. If panic_on_ue is set
|
||
this counter will not have a chance to increment, since EDAC
|
||
will panic the system.
|
||
|
||
- ``dimm_ce_count`` - Correctable Errors count attribute file
|
||
|
||
This attribute file displays the total count of correctable
|
||
errors that have occurred on this DIMM. This count is very
|
||
important to examine. CEs provide early indications that a
|
||
DIMM is beginning to fail. This count field should be
|
||
monitored for non-zero values and report such information
|
||
to the system administrator.
|
||
|
||
- ``dimm_dev_type`` - Device type attribute file
|
||
|
||
This attribute file will display what type of DRAM device is
|
||
being utilized on this DIMM.
|
||
Examples:
|
||
|
||
- x1
|
||
- x2
|
||
- x4
|
||
- x8
|
||
|
||
- ``dimm_edac_mode`` - EDAC Mode of operation attribute file
|
||
|
||
This attribute file will display what type of Error detection
|
||
and correction is being utilized.
|
||
|
||
- ``dimm_label`` - memory module label control file
|
||
|
||
This control file allows this DIMM to have a label assigned
|
||
to it. With this label in the module, when errors occur
|
||
the output can provide the DIMM label in the system log.
|
||
This becomes vital for panic events to isolate the
|
||
cause of the UE event.
|
||
|
||
DIMM Labels must be assigned after booting, with information
|
||
that correctly identifies the physical slot with its
|
||
silk screen label. This information is currently very
|
||
motherboard specific and determination of this information
|
||
must occur in userland at this time.
|
||
|
||
- ``dimm_location`` - location of the memory module
|
||
|
||
The location can have up to 3 levels, and describe how the
|
||
memory controller identifies the location of a memory module.
|
||
Depending on the type of memory and memory controller, it
|
||
can be:
|
||
|
||
- *csrow* and *channel* - used when the memory controller
|
||
doesn't identify a single DIMM - e. g. in ``rankX`` dir;
|
||
- *branch*, *channel*, *slot* - typically used on FB-DIMM memory
|
||
controllers;
|
||
- *channel*, *slot* - used on Nehalem and newer Intel drivers.
|
||
|
||
- ``dimm_mem_type`` - Memory Type attribute file
|
||
|
||
This attribute file will display what type of memory is currently
|
||
on this csrow. Normally, either buffered or unbuffered memory.
|
||
Examples:
|
||
|
||
- Registered-DDR
|
||
- Unbuffered-DDR
|
||
|
||
.. [#f5] On some systems, the memory controller doesn't have any logic
|
||
to identify the memory module. On such systems, the directory is called ``rankX`` and works on a similar way as the ``csrowX`` directories.
|
||
On modern Intel memory controllers, the memory controller identifies the
|
||
memory modules directly. On such systems, the directory is called ``dimmX``.
|
||
|
||
.. [#f6] There are also some ``power`` directories and ``subsystem``
|
||
symlinks inside the sysfs mapping that are automatically created by
|
||
the sysfs subsystem. Currently, they serve no purpose.
|
||
|
||
``csrowX`` directories
|
||
----------------------
|
||
|
||
When CONFIG_EDAC_LEGACY_SYSFS is enabled, sysfs will contain the ``csrowX``
|
||
directories. As this API doesn't work properly for Rambus, FB-DIMMs and
|
||
modern Intel Memory Controllers, this is being deprecated in favor of
|
||
``dimmX`` directories.
|
||
|
||
In the ``csrowX`` directories are EDAC control and attribute files for
|
||
this ``X`` instance of csrow:
|
||
|
||
|
||
- ``ue_count`` - Total Uncorrectable Errors count attribute file
|
||
|
||
This attribute file displays the total count of uncorrectable
|
||
errors that have occurred on this csrow. If panic_on_ue is set
|
||
this counter will not have a chance to increment, since EDAC
|
||
will panic the system.
|
||
|
||
|
||
- ``ce_count`` - Total Correctable Errors count attribute file
|
||
|
||
This attribute file displays the total count of correctable
|
||
errors that have occurred on this csrow. This count is very
|
||
important to examine. CEs provide early indications that a
|
||
DIMM is beginning to fail. This count field should be
|
||
monitored for non-zero values and report such information
|
||
to the system administrator.
|
||
|
||
|
||
- ``size_mb`` - Total memory managed by this csrow attribute file
|
||
|
||
This attribute file displays, in count of megabytes, the memory
|
||
that this csrow contains.
|
||
|
||
|
||
- ``mem_type`` - Memory Type attribute file
|
||
|
||
This attribute file will display what type of memory is currently
|
||
on this csrow. Normally, either buffered or unbuffered memory.
|
||
Examples:
|
||
|
||
- Registered-DDR
|
||
- Unbuffered-DDR
|
||
|
||
|
||
- ``edac_mode`` - EDAC Mode of operation attribute file
|
||
|
||
This attribute file will display what type of Error detection
|
||
and correction is being utilized.
|
||
|
||
|
||
- ``dev_type`` - Device type attribute file
|
||
|
||
This attribute file will display what type of DRAM device is
|
||
being utilized on this DIMM.
|
||
Examples:
|
||
|
||
- x1
|
||
- x2
|
||
- x4
|
||
- x8
|
||
|
||
|
||
- ``ch0_ce_count`` - Channel 0 CE Count attribute file
|
||
|
||
This attribute file will display the count of CEs on this
|
||
DIMM located in channel 0.
|
||
|
||
|
||
- ``ch0_ue_count`` - Channel 0 UE Count attribute file
|
||
|
||
This attribute file will display the count of UEs on this
|
||
DIMM located in channel 0.
|
||
|
||
|
||
- ``ch0_dimm_label`` - Channel 0 DIMM Label control file
|
||
|
||
|
||
This control file allows this DIMM to have a label assigned
|
||
to it. With this label in the module, when errors occur
|
||
the output can provide the DIMM label in the system log.
|
||
This becomes vital for panic events to isolate the
|
||
cause of the UE event.
|
||
|
||
DIMM Labels must be assigned after booting, with information
|
||
that correctly identifies the physical slot with its
|
||
silk screen label. This information is currently very
|
||
motherboard specific and determination of this information
|
||
must occur in userland at this time.
|
||
|
||
|
||
- ``ch1_ce_count`` - Channel 1 CE Count attribute file
|
||
|
||
|
||
This attribute file will display the count of CEs on this
|
||
DIMM located in channel 1.
|
||
|
||
|
||
- ``ch1_ue_count`` - Channel 1 UE Count attribute file
|
||
|
||
|
||
This attribute file will display the count of UEs on this
|
||
DIMM located in channel 0.
|
||
|
||
|
||
- ``ch1_dimm_label`` - Channel 1 DIMM Label control file
|
||
|
||
This control file allows this DIMM to have a label assigned
|
||
to it. With this label in the module, when errors occur
|
||
the output can provide the DIMM label in the system log.
|
||
This becomes vital for panic events to isolate the
|
||
cause of the UE event.
|
||
|
||
DIMM Labels must be assigned after booting, with information
|
||
that correctly identifies the physical slot with its
|
||
silk screen label. This information is currently very
|
||
motherboard specific and determination of this information
|
||
must occur in userland at this time.
|
||
|
||
|
||
System Logging
|
||
--------------
|
||
|
||
If logging for UEs and CEs is enabled, then system logs will contain
|
||
information indicating that errors have been detected::
|
||
|
||
EDAC MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0, channel 1 "DIMM_B1": amd76x_edac
|
||
EDAC MC0: CE page 0x1e5, offset 0xfb0, grain 8, syndrome 0xb741, row 0, channel 1 "DIMM_B1": amd76x_edac
|
||
|
||
|
||
The structure of the message is:
|
||
|
||
+---------------------------------------+-------------+
|
||
| Content | Example |
|
||
+=======================================+=============+
|
||
| The memory controller | MC0 |
|
||
+---------------------------------------+-------------+
|
||
| Error type | CE |
|
||
+---------------------------------------+-------------+
|
||
| Memory page | 0x283 |
|
||
+---------------------------------------+-------------+
|
||
| Offset in the page | 0xce0 |
|
||
+---------------------------------------+-------------+
|
||
| The byte granularity | grain 8 |
|
||
| or resolution of the error | |
|
||
+---------------------------------------+-------------+
|
||
| The error syndrome | 0xb741 |
|
||
+---------------------------------------+-------------+
|
||
| Memory row | row 0 |
|
||
+---------------------------------------+-------------+
|
||
| Memory channel | channel 1 |
|
||
+---------------------------------------+-------------+
|
||
| DIMM label, if set prior | DIMM B1 |
|
||
+---------------------------------------+-------------+
|
||
| And then an optional, driver-specific | |
|
||
| message that may have additional | |
|
||
| information. | |
|
||
+---------------------------------------+-------------+
|
||
|
||
Both UEs and CEs with no info will lack all but memory controller, error
|
||
type, a notice of "no info" and then an optional, driver-specific error
|
||
message.
|
||
|
||
|
||
PCI Bus Parity Detection
|
||
------------------------
|
||
|
||
On Header Type 00 devices, the primary status is looked at for any
|
||
parity error regardless of whether parity is enabled on the device or
|
||
not. (The spec indicates parity is generated in some cases). On Header
|
||
Type 01 bridges, the secondary status register is also looked at to see
|
||
if parity occurred on the bus on the other side of the bridge.
|
||
|
||
|
||
Sysfs configuration
|
||
-------------------
|
||
|
||
Under ``/sys/devices/system/edac/pci`` are control and attribute files as
|
||
follows:
|
||
|
||
|
||
- ``check_pci_parity`` - Enable/Disable PCI Parity checking control file
|
||
|
||
This control file enables or disables the PCI Bus Parity scanning
|
||
operation. Writing a 1 to this file enables the scanning. Writing
|
||
a 0 to this file disables the scanning.
|
||
|
||
Enable::
|
||
|
||
echo "1" >/sys/devices/system/edac/pci/check_pci_parity
|
||
|
||
Disable::
|
||
|
||
echo "0" >/sys/devices/system/edac/pci/check_pci_parity
|
||
|
||
|
||
- ``pci_parity_count`` - Parity Count
|
||
|
||
This attribute file will display the number of parity errors that
|
||
have been detected.
|
||
|
||
|
||
Module parameters
|
||
-----------------
|
||
|
||
- ``edac_mc_panic_on_ue`` - Panic on UE control file
|
||
|
||
An uncorrectable error will cause a machine panic. This is usually
|
||
desirable. It is a bad idea to continue when an uncorrectable error
|
||
occurs - it is indeterminate what was uncorrected and the operating
|
||
system context might be so mangled that continuing will lead to further
|
||
corruption. If the kernel has MCE configured, then EDAC will never
|
||
notice the UE.
|
||
|
||
LOAD TIME::
|
||
|
||
module/kernel parameter: edac_mc_panic_on_ue=[0|1]
|
||
|
||
RUN TIME::
|
||
|
||
echo "1" > /sys/module/edac_core/parameters/edac_mc_panic_on_ue
|
||
|
||
|
||
- ``edac_mc_log_ue`` - Log UE control file
|
||
|
||
|
||
Generate kernel messages describing uncorrectable errors. These errors
|
||
are reported through the system message log system. UE statistics
|
||
will be accumulated even when UE logging is disabled.
|
||
|
||
LOAD TIME::
|
||
|
||
module/kernel parameter: edac_mc_log_ue=[0|1]
|
||
|
||
RUN TIME::
|
||
|
||
echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ue
|
||
|
||
|
||
- ``edac_mc_log_ce`` - Log CE control file
|
||
|
||
|
||
Generate kernel messages describing correctable errors. These
|
||
errors are reported through the system message log system.
|
||
CE statistics will be accumulated even when CE logging is disabled.
|
||
|
||
LOAD TIME::
|
||
|
||
module/kernel parameter: edac_mc_log_ce=[0|1]
|
||
|
||
RUN TIME::
|
||
|
||
echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ce
|
||
|
||
|
||
- ``edac_mc_poll_msec`` - Polling period control file
|
||
|
||
|
||
The time period, in milliseconds, for polling for error information.
|
||
Too small a value wastes resources. Too large a value might delay
|
||
necessary handling of errors and might loose valuable information for
|
||
locating the error. 1000 milliseconds (once each second) is the current
|
||
default. Systems which require all the bandwidth they can get, may
|
||
increase this.
|
||
|
||
LOAD TIME::
|
||
|
||
module/kernel parameter: edac_mc_poll_msec=[0|1]
|
||
|
||
RUN TIME::
|
||
|
||
echo "1000" > /sys/module/edac_core/parameters/edac_mc_poll_msec
|
||
|
||
|
||
- ``panic_on_pci_parity`` - Panic on PCI PARITY Error
|
||
|
||
|
||
This control file enables or disables panicking when a parity
|
||
error has been detected.
|
||
|
||
|
||
module/kernel parameter::
|
||
|
||
edac_panic_on_pci_pe=[0|1]
|
||
|
||
Enable::
|
||
|
||
echo "1" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
|
||
|
||
Disable::
|
||
|
||
echo "0" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
|
||
|
||
|
||
|
||
EDAC device type
|
||
----------------
|
||
|
||
In the header file, edac_pci.h, there is a series of edac_device structures
|
||
and APIs for the EDAC_DEVICE.
|
||
|
||
User space access to an edac_device is through the sysfs interface.
|
||
|
||
At the location ``/sys/devices/system/edac`` (sysfs) new edac_device devices
|
||
will appear.
|
||
|
||
There is a three level tree beneath the above ``edac`` directory. For example,
|
||
the ``test_device_edac`` device (found at the http://bluesmoke.sourceforget.net
|
||
website) installs itself as::
|
||
|
||
/sys/devices/system/edac/test-instance
|
||
|
||
in this directory are various controls, a symlink and one or more ``instance``
|
||
directories.
|
||
|
||
The standard default controls are:
|
||
|
||
============== =======================================================
|
||
log_ce boolean to log CE events
|
||
log_ue boolean to log UE events
|
||
panic_on_ue boolean to ``panic`` the system if an UE is encountered
|
||
(default off, can be set true via startup script)
|
||
poll_msec time period between POLL cycles for events
|
||
============== =======================================================
|
||
|
||
The test_device_edac device adds at least one of its own custom control:
|
||
|
||
============== ==================================================
|
||
test_bits which in the current test driver does nothing but
|
||
show how it is installed. A ported driver can
|
||
add one or more such controls and/or attributes
|
||
for specific uses.
|
||
One out-of-tree driver uses controls here to allow
|
||
for ERROR INJECTION operations to hardware
|
||
injection registers
|
||
============== ==================================================
|
||
|
||
The symlink points to the 'struct dev' that is registered for this edac_device.
|
||
|
||
Instances
|
||
---------
|
||
|
||
One or more instance directories are present. For the ``test_device_edac``
|
||
case:
|
||
|
||
+----------------+
|
||
| test-instance0 |
|
||
+----------------+
|
||
|
||
|
||
In this directory there are two default counter attributes, which are totals of
|
||
counter in deeper subdirectories.
|
||
|
||
============== ====================================
|
||
ce_count total of CE events of subdirectories
|
||
ue_count total of UE events of subdirectories
|
||
============== ====================================
|
||
|
||
Blocks
|
||
------
|
||
|
||
At the lowest directory level is the ``block`` directory. There can be 0, 1
|
||
or more blocks specified in each instance:
|
||
|
||
+-------------+
|
||
| test-block0 |
|
||
+-------------+
|
||
|
||
In this directory the default attributes are:
|
||
|
||
============== ================================================
|
||
ce_count which is counter of CE events for this ``block``
|
||
of hardware being monitored
|
||
ue_count which is counter of UE events for this ``block``
|
||
of hardware being monitored
|
||
============== ================================================
|
||
|
||
|
||
The ``test_device_edac`` device adds 4 attributes and 1 control:
|
||
|
||
================== ====================================================
|
||
test-block-bits-0 for every POLL cycle this counter
|
||
is incremented
|
||
test-block-bits-1 every 10 cycles, this counter is bumped once,
|
||
and test-block-bits-0 is set to 0
|
||
test-block-bits-2 every 100 cycles, this counter is bumped once,
|
||
and test-block-bits-1 is set to 0
|
||
test-block-bits-3 every 1000 cycles, this counter is bumped once,
|
||
and test-block-bits-2 is set to 0
|
||
================== ====================================================
|
||
|
||
|
||
================== ====================================================
|
||
reset-counters writing ANY thing to this control will
|
||
reset all the above counters.
|
||
================== ====================================================
|
||
|
||
|
||
Use of the ``test_device_edac`` driver should enable any others to create their own
|
||
unique drivers for their hardware systems.
|
||
|
||
The ``test_device_edac`` sample driver is located at the
|
||
http://bluesmoke.sourceforge.net project site for EDAC.
|
||
|
||
|
||
Usage of EDAC APIs on Nehalem and newer Intel CPUs
|
||
--------------------------------------------------
|
||
|
||
On older Intel architectures, the memory controller was part of the North
|
||
Bridge chipset. Nehalem, Sandy Bridge, Ivy Bridge, Haswell, Sky Lake and
|
||
newer Intel architectures integrated an enhanced version of the memory
|
||
controller (MC) inside the CPUs.
|
||
|
||
This chapter will cover the differences of the enhanced memory controllers
|
||
found on newer Intel CPUs, such as ``i7core_edac``, ``sb_edac`` and
|
||
``sbx_edac`` drivers.
|
||
|
||
.. note::
|
||
|
||
The Xeon E7 processor families use a separate chip for the memory
|
||
controller, called Intel Scalable Memory Buffer. This section doesn't
|
||
apply for such families.
|
||
|
||
1) There is one Memory Controller per Quick Patch Interconnect
|
||
(QPI). At the driver, the term "socket" means one QPI. This is
|
||
associated with a physical CPU socket.
|
||
|
||
Each MC have 3 physical read channels, 3 physical write channels and
|
||
3 logic channels. The driver currently sees it as just 3 channels.
|
||
Each channel can have up to 3 DIMMs.
|
||
|
||
The minimum known unity is DIMMs. There are no information about csrows.
|
||
As EDAC API maps the minimum unity is csrows, the driver sequentially
|
||
maps channel/DIMM into different csrows.
|
||
|
||
For example, supposing the following layout::
|
||
|
||
Ch0 phy rd0, wr0 (0x063f4031): 2 ranks, UDIMMs
|
||
dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
|
||
dimm 1 1024 Mb offset: 4, bank: 8, rank: 1, row: 0x4000, col: 0x400
|
||
Ch1 phy rd1, wr1 (0x063f4031): 2 ranks, UDIMMs
|
||
dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
|
||
Ch2 phy rd3, wr3 (0x063f4031): 2 ranks, UDIMMs
|
||
dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
|
||
|
||
The driver will map it as::
|
||
|
||
csrow0: channel 0, dimm0
|
||
csrow1: channel 0, dimm1
|
||
csrow2: channel 1, dimm0
|
||
csrow3: channel 2, dimm0
|
||
|
||
exports one DIMM per csrow.
|
||
|
||
Each QPI is exported as a different memory controller.
|
||
|
||
2) The MC has the ability to inject errors to test drivers. The drivers
|
||
implement this functionality via some error injection nodes:
|
||
|
||
For injecting a memory error, there are some sysfs nodes, under
|
||
``/sys/devices/system/edac/mc/mc?/``:
|
||
|
||
- ``inject_addrmatch/*``:
|
||
Controls the error injection mask register. It is possible to specify
|
||
several characteristics of the address to match an error code::
|
||
|
||
dimm = the affected dimm. Numbers are relative to a channel;
|
||
rank = the memory rank;
|
||
channel = the channel that will generate an error;
|
||
bank = the affected bank;
|
||
page = the page address;
|
||
column (or col) = the address column.
|
||
|
||
each of the above values can be set to "any" to match any valid value.
|
||
|
||
At driver init, all values are set to any.
|
||
|
||
For example, to generate an error at rank 1 of dimm 2, for any channel,
|
||
any bank, any page, any column::
|
||
|
||
echo 2 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/dimm
|
||
echo 1 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/rank
|
||
|
||
To return to the default behaviour of matching any, you can do::
|
||
|
||
echo any >/sys/devices/system/edac/mc/mc0/inject_addrmatch/dimm
|
||
echo any >/sys/devices/system/edac/mc/mc0/inject_addrmatch/rank
|
||
|
||
- ``inject_eccmask``:
|
||
specifies what bits will have troubles,
|
||
|
||
- ``inject_section``:
|
||
specifies what ECC cache section will get the error::
|
||
|
||
3 for both
|
||
2 for the highest
|
||
1 for the lowest
|
||
|
||
- ``inject_type``:
|
||
specifies the type of error, being a combination of the following bits::
|
||
|
||
bit 0 - repeat
|
||
bit 1 - ecc
|
||
bit 2 - parity
|
||
|
||
- ``inject_enable``:
|
||
starts the error generation when something different than 0 is written.
|
||
|
||
All inject vars can be read. root permission is needed for write.
|
||
|
||
Datasheet states that the error will only be generated after a write on an
|
||
address that matches inject_addrmatch. It seems, however, that reading will
|
||
also produce an error.
|
||
|
||
For example, the following code will generate an error for any write access
|
||
at socket 0, on any DIMM/address on channel 2::
|
||
|
||
echo 2 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/channel
|
||
echo 2 >/sys/devices/system/edac/mc/mc0/inject_type
|
||
echo 64 >/sys/devices/system/edac/mc/mc0/inject_eccmask
|
||
echo 3 >/sys/devices/system/edac/mc/mc0/inject_section
|
||
echo 1 >/sys/devices/system/edac/mc/mc0/inject_enable
|
||
dd if=/dev/mem of=/dev/null seek=16k bs=4k count=1 >& /dev/null
|
||
|
||
For socket 1, it is needed to replace "mc0" by "mc1" at the above
|
||
commands.
|
||
|
||
The generated error message will look like::
|
||
|
||
EDAC MC0: UE row 0, channel-a= 0 channel-b= 0 labels "-": NON_FATAL (addr = 0x0075b980, socket=0, Dimm=0, Channel=2, syndrome=0x00000040, count=1, Err=8c0000400001009f:4000080482 (read error: read ECC error))
|
||
|
||
3) Corrected Error memory register counters
|
||
|
||
Those newer MCs have some registers to count memory errors. The driver
|
||
uses those registers to report Corrected Errors on devices with Registered
|
||
DIMMs.
|
||
|
||
However, those counters don't work with Unregistered DIMM. As the chipset
|
||
offers some counters that also work with UDIMMs (but with a worse level of
|
||
granularity than the default ones), the driver exposes those registers for
|
||
UDIMM memories.
|
||
|
||
They can be read by looking at the contents of ``all_channel_counts/``::
|
||
|
||
$ for i in /sys/devices/system/edac/mc/mc0/all_channel_counts/*; do echo $i; cat $i; done
|
||
/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm0
|
||
0
|
||
/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm1
|
||
0
|
||
/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm2
|
||
0
|
||
|
||
What happens here is that errors on different csrows, but at the same
|
||
dimm number will increment the same counter.
|
||
So, in this memory mapping::
|
||
|
||
csrow0: channel 0, dimm0
|
||
csrow1: channel 0, dimm1
|
||
csrow2: channel 1, dimm0
|
||
csrow3: channel 2, dimm0
|
||
|
||
The hardware will increment udimm0 for an error at the first dimm at either
|
||
csrow0, csrow2 or csrow3;
|
||
|
||
The hardware will increment udimm1 for an error at the second dimm at either
|
||
csrow0, csrow2 or csrow3;
|
||
|
||
The hardware will increment udimm2 for an error at the third dimm at either
|
||
csrow0, csrow2 or csrow3;
|
||
|
||
4) Standard error counters
|
||
|
||
The standard error counters are generated when an mcelog error is received
|
||
by the driver. Since, with UDIMM, this is counted by software, it is
|
||
possible that some errors could be lost. With RDIMM's, they display the
|
||
contents of the registers
|
||
|
||
Reference documents used on ``amd64_edac``
|
||
------------------------------------------
|
||
|
||
``amd64_edac`` module is based on the following documents
|
||
(available from http://support.amd.com/en-us/search/tech-docs):
|
||
|
||
1. :Title: BIOS and Kernel Developer's Guide for AMD Athlon 64 and AMD
|
||
Opteron Processors
|
||
:AMD publication #: 26094
|
||
:Revision: 3.26
|
||
:Link: http://support.amd.com/TechDocs/26094.PDF
|
||
|
||
2. :Title: BIOS and Kernel Developer's Guide for AMD NPT Family 0Fh
|
||
Processors
|
||
:AMD publication #: 32559
|
||
:Revision: 3.00
|
||
:Issue Date: May 2006
|
||
:Link: http://support.amd.com/TechDocs/32559.pdf
|
||
|
||
3. :Title: BIOS and Kernel Developer's Guide (BKDG) For AMD Family 10h
|
||
Processors
|
||
:AMD publication #: 31116
|
||
:Revision: 3.00
|
||
:Issue Date: September 07, 2007
|
||
:Link: http://support.amd.com/TechDocs/31116.pdf
|
||
|
||
4. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 15h
|
||
Models 30h-3Fh Processors
|
||
:AMD publication #: 49125
|
||
:Revision: 3.06
|
||
:Issue Date: 2/12/2015 (latest release)
|
||
:Link: http://support.amd.com/TechDocs/49125_15h_Models_30h-3Fh_BKDG.pdf
|
||
|
||
5. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 15h
|
||
Models 60h-6Fh Processors
|
||
:AMD publication #: 50742
|
||
:Revision: 3.01
|
||
:Issue Date: 7/23/2015 (latest release)
|
||
:Link: http://support.amd.com/TechDocs/50742_15h_Models_60h-6Fh_BKDG.pdf
|
||
|
||
6. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 16h
|
||
Models 00h-0Fh Processors
|
||
:AMD publication #: 48751
|
||
:Revision: 3.03
|
||
:Issue Date: 2/23/2015 (latest release)
|
||
:Link: http://support.amd.com/TechDocs/48751_16h_bkdg.pdf
|
||
|
||
Credits
|
||
=======
|
||
|
||
* Written by Doug Thompson <dougthompson@xmission.com>
|
||
|
||
- 7 Dec 2005
|
||
- 17 Jul 2007 Updated
|
||
|
||
* |copy| Mauro Carvalho Chehab
|
||
|
||
- 05 Aug 2009 Nehalem interface
|
||
- 26 Oct 2016 Converted to ReST and cleanups at the Nehalem section
|
||
|
||
* EDAC authors/maintainers:
|
||
|
||
- Doug Thompson, Dave Jiang, Dave Peterson et al,
|
||
- Mauro Carvalho Chehab
|
||
- Borislav Petkov
|
||
- original author: Thayne Harbaugh
|