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Stephane Eranian 83bd6d1212 perf/x86/intel/uncore: Fix broken read_counter() for SNB IMC PMU 
commit 11745ecfe8 upstream.

Existing code was generating bogus counts for the SNB IMC bandwidth counters:

$ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
     1.000327813           1,024.03 MiB  uncore_imc/data_reads/
     1.000327813              20.73 MiB  uncore_imc/data_writes/
     2.000580153         261,120.00 MiB  uncore_imc/data_reads/
     2.000580153              23.28 MiB  uncore_imc/data_writes/

The problem was introduced by commit:
  07ce734dd8 ("perf/x86/intel/uncore: Clean up client IMC")

Where the read_counter callback was replace to point to the generic
uncore_mmio_read_counter() function.

The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
MMIO therefore reading 64-bit from MMIO. Although this is okay for the
uncore_perf_event_update() function because it is shifting the value based
on the actual counter width to compute a delta, it is not okay for the
uncore_pmu_event_start() which is simply reading the counter  and therefore
priming the event->prev_count with a bogus value which is responsible for
causing bogus deltas in the perf stat command above.

The fix is to reintroduce the custom callback for read_counter for the SNB
IMC PMU and use readl() instead of readq(). With the change the output of
perf stat is back to normal:
$ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
     1.000120987             296.94 MiB  uncore_imc/data_reads/
     1.000120987             138.42 MiB  uncore_imc/data_writes/
     2.000403144             175.91 MiB  uncore_imc/data_reads/
     2.000403144              68.50 MiB  uncore_imc/data_writes/

Fixes: 07ce734dd8 ("perf/x86/intel/uncore: Clean up client IMC")
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20220803160031.1379788-1-eranian@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-08-31 17:16:51 +02:00
arch perf/x86/intel/uncore: Fix broken read_counter() for SNB IMC PMU 2022-08-31 17:16:51 +02:00
block blk-mq: fix io hung due to missing commit_rqs 2022-08-31 17:16:50 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto KEYS: asymmetric: enforce SM2 signature use pkey algo 2022-08-17 14:24:28 +02:00
Documentation Documentation/ABI: Mention retbleed vulnerability info file for sysfs 2022-08-31 17:16:50 +02:00
drivers binder_alloc: add missing mmap_lock calls when using the VMA 2022-08-31 17:16:50 +02:00
fs io_uring: fix issue with io_write() not always undoing sb_start_write() 2022-08-31 17:16:49 +02:00
include Revert "memcg: cleanup racy sum avoidance code" 2022-08-31 17:16:48 +02:00
init stack: Declare {randomize_,}kstack_offset to fix Sparse warnings 2022-08-17 14:23:10 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:23:10 +02:00
kernel kernel/sys_ni: add compat entry for fadvise64_64 2022-08-31 17:16:33 +02:00
lib ratelimit: Fix data-races in ___ratelimit(). 2022-08-31 17:16:43 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/hugetlb: fix hugetlb not supporting softdirty tracking 2022-08-31 17:16:49 +02:00
net mptcp: Fix crash due to tcp_tsorted_anchor was initialized before release skb 2022-08-31 17:16:50 +02:00
samples samples/landlock: Format with clang-format 2022-06-09 10:23:23 +02:00
scripts modules: Ensure natural alignment for .altinstructions and __bug_table sections 2022-08-25 11:40:41 +02:00
security apparmor: Fix memleak in aa_simple_write_to_buffer() 2022-08-25 11:40:01 +02:00
sound ALSA: control: Use deferred fasync helper 2022-08-25 11:40:44 +02:00
tools perf python: Fix build when PYTHON_CONFIG is user supplied 2022-08-31 17:16:51 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Unconditionally get a ref to /dev/kvm module when creating a VM 2022-08-25 11:39:53 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Input: goodix - add a goodix.h header file 2022-07-12 16:34:51 +02:00
Makefile Linux 5.15.63 2022-08-25 11:40:49 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.