Paul E. McKenney 73af8425a5 clocksource: Retry clock read if long delays detected ... [ Upstream commit db3a34e174 ] When the clocksource watchdog marks a clock as unstable, this might be due to that clock being unstable or it might be due to delays that happen to occur between the reads of the two clocks. Yes, interrupts are disabled across those two reads, but there are no shortage of things that can delay interrupts-disabled regions of code ranging from SMI handlers to vCPU preemption. It would be good to have some indication as to why the clock was marked unstable. Therefore, re-read the watchdog clock on either side of the read from the clock under test. If the watchdog clock shows an excessive time delta between its pair of reads, the reads are retried. The maximum number of retries is specified by a new kernel boot parameter clocksource.max_cswd_read_retries, which defaults to three, that is, up to four reads, one initial and up to three retries. If more than one retry was required, a message is printed on the console (the occasional single retry is expected behavior, especially in guest OSes). If the maximum number of retries is exceeded, the clock under test will be marked unstable. However, the probability of this happening due to various sorts of delays is quite small. In addition, the reason (clock-read delays) for the unstable marking will be apparent. Reported-by: Chris Mason <clm@fb.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Feng Tang <feng.tang@intel.com> Link: https://lore.kernel.org/r/20210527190124.440372-1-paulmck@kernel.org Signed-off-by: Sasha Levin <sashal@kernel.org>		2021-07-20 16:15:46 +02:00
..
ABI	evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded	2021-07-20 16:15:42 +02:00
accelerators	ocxl: Document new OCXL IOCTLs	2018-06-03 20:40:33 +10:00
accounting
acpi	ACPI: property: graph: Update graph documentation to use generic references	2018-07-23 12:44:52 +02:00
admin-guide	clocksource: Retry clock read if long delays detected	2021-07-20 16:15:46 +02:00
aoe
arm	ARM: 8833/1: Ensure that NEON code always compiles with Clang	2019-04-05 22:33:08 +02:00
arm64	arm64: errata: Hide CTR_EL0.DIC on systems affected by Neoverse-N1 #1542419	2020-04-29 16:31:08 +02:00
auxdisplay
backlight
block	block: Track DISCARD statistics and output them in stat and diskstat	2018-07-18 08:44:22 -06:00
blockdev	zram: introduce zram memory tracking	2018-06-07 17:34:34 -07:00
bpf	Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next	2018-08-07 11:02:05 -07:00
bus-devices
cdrom
cgroup-v1
cma
connector
console	Documentation: corrections to console/console.txt	2018-08-10 16:09:40 -06:00
core-api	idr: Change documentation license	2018-10-15 16:31:29 -04:00
cpu-freq
cpuidle
crypto	crypto: remove redundant type flags from tfm allocation	2018-07-09 00:30:29 +08:00
dev-tools	doc: dev-tools: kselftest.rst: update contributing new tests	2018-06-29 09:01:50 -06:00
device-mapper	dm integrity: conditionally disable "recalculate" feature	2021-01-30 13:32:13 +01:00
devicetree	dt-bindings: net: btusb: DT fix s/interrupt-name/interrupt-names/	2021-03-07 12:18:56 +01:00
doc-guide	Documentation/sphinx: allow "functions" with no parameters	2018-06-30 07:52:42 -06:00
driver-api	ata: make qc_prep return ata_completion_errors	2020-10-01 13:14:54 +02:00
driver-model	dmaengine: add a new helper dmaenginem_async_device_register	2018-07-30 10:50:22 +05:30
early-userspace	initramfs: move gen_initramfs_list.sh from scripts/ to usr/	2018-08-22 23:21:44 +09:00
EDID
extcon
fault-injection
fb	uvesafb: Fix URLs in the documentation	2018-09-26 18:11:23 +02:00
features	ARM: 8777/1: Hook up SYNC_CORE functionality for sys_membarrier()	2018-07-11 11:02:08 +01:00
filesystems	sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output	2021-03-07 12:19:01 +01:00
firmware_class
fmc
fpga	docs: fpga: add a document for FPGA Device Feature List (DFL) Framework Overview	2018-07-15 13:55:44 +02:00
gpio
gpu	drm/msm/gpu: Add the buffer objects from the submit to the crash dump	2018-07-30 08:50:10 -04:00
hid	HID: doc: fix wrong data structure reference for UHID_OUTPUT	2019-12-05 09:20:36 +01:00
hwmon	hwmon: (ina2xx) fix sysfs shunt resistor read access	2018-08-26 17:45:25 -07:00
i2c	i2c: i801: Add support for Intel Comet Lake	2019-05-04 09:20:15 +02:00
ia64
ide
iio
infiniband
input	input: add MT_TOOL_DIAL	2018-07-17 15:33:47 +02:00
ioctl	Char/Misc driver patches for 4.19-rc1	2018-08-18 11:04:51 -07:00
isdn
kbuild	kbuild: support LLVM=1 to switch the default tools to Clang/LLVM	2020-09-26 18:01:32 +02:00
kdump
kernel-hacking	doc:it_IT: translation for kernel-hacking	2018-07-26 16:21:09 -06:00
laptops
leds
lightnvm
livepatch
locking	locking: Implement an algorithm choice for Wound-Wait mutexes	2018-07-03 09:44:36 +02:00
m68k
maintainer	docs: Fix more broken references	2018-06-15 18:11:26 -03:00
md
media	media: videodev2.h: RGB BT2020 and HSV are always full range	2020-11-05 11:08:40 +01:00
memory-devices
mic
mips
misc-devices	pci_endpoint_test: Add 2 ioctl commands	2018-07-19 11:46:57 +01:00
mmc
mtd
namespaces
netlabel
networking	icmp: randomize the global rate limiter	2020-10-29 09:54:58 +01:00
nfc
nios2
nvdimm
nvmem
openrisc
parisc
PCI	Merge branch 'remotes/lorenzo/pci/dwc'	2018-08-15 14:59:11 -05:00
pcmcia	pcmcia: remove long deprecated pcmcia_request_exclusive_irq() function	2018-08-18 12:30:42 -07:00
perf
phy
platform
power	PM / reboot: Eliminate race between reboot and suspend	2018-08-06 12:35:20 +02:00
powerpc	powerpc: Document issues with TM on POWER9	2018-07-02 23:54:29 +10:00
pps
process	stable-kernel-rules.rst: add link to networking patch queue	2019-03-23 20:10:10 +01:00
pti
ptp
rapidio
RCU	rculist: Improve documentation for list_for_each_entry_from_rcu()	2018-07-12 15:39:25 -07:00
riscv	perf: riscv: Add Document for Future Porting Guide	2018-06-04 14:02:11 -07:00
s390
scheduler	sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices	2019-11-12 19:20:50 +01:00
scsi	scsi: documentation: add scsi_mod.use_blk_mq to scsi-parameters	2018-08-27 12:26:10 -04:00
security	Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables	2018-06-14 12:21:18 +09:00
serial
sh
sound	ALSA: hda/realtek - Remove now-unnecessary XPS 13 headphone noise fixups	2020-04-17 10:48:45 +02:00
sparc
sphinx	tweewide: Fix most Shebang lines	2021-05-22 10:59:50 +02:00
sphinx-static
spi
sysctl	bpf: add bpf_jit_limit knob to restrict unpriv allocations	2019-05-31 06:46:03 -07:00
target	tweewide: Fix most Shebang lines	2021-05-22 10:59:50 +02:00
thermal
timers	timekeeping.txt: Correct maxCount of n-bit binary counter	2018-07-23 09:33:06 -06:00
trace	tweewide: Fix most Shebang lines	2021-05-22 10:59:50 +02:00
translations	This was a moderately busy cycle for docs, with the usual collection of	2018-08-14 14:29:31 -07:00
usb	USB: rio500: Remove Rio 500 kernel driver	2019-10-17 13:44:47 -07:00
userspace-api	Documentation: Add section about CPU vulnerabilities for Spectre	2019-07-14 08:11:17 +02:00
virtual	x86/kvm/hyper-v: Explicitly align hcall param for kvm_hyperv_exit	2020-06-22 09:05:12 +02:00
vm	mm/slub: clarify verification reporting	2021-06-30 08:48:26 -04:00
w1	w1: fix w1_ds2438 documentation	2018-07-07 17:27:13 +02:00
watchdog
wimax
x86	x86/speculation/taa: Add documentation for TSX Async Abort	2019-11-12 19:21:34 +01:00
xtensa
.gitignore
00-INDEX
atomic_bitops.txt
atomic_t.txt	x86/atomic: Fix smp_mb__{before,after}_atomic()	2019-07-26 09:14:08 +02:00
bt8xxgpio.txt
btmrvl.txt
bus-virt-phys-mapping.txt
Changes
clearing-warn-once.txt
CodingStyle
conf.py	docs: Fix conf.py for Sphinx 2.0	2019-06-09 09:17:20 +02:00
cpu-load.txt
cputopology.txt
crc32.txt
dcdbas.txt
debugging-modules.txt
debugging-via-ohci1394.txt
dell_rbu.txt
digsig.txt
DMA-API-HOWTO.txt
DMA-API.txt
DMA-attributes.txt
DMA-ISA-LPC.txt
docutils.conf
dontdiff
efi-stub.txt
eisa.txt
flexible-arrays.txt
futex-requeue-pi.txt
gcc-plugins.txt
highuid.txt
hw_random.txt
hwspinlock.txt
index.rst	x86/speculation/mds: Add mds_clear_cpu_buffers()	2019-05-14 19:17:54 +02:00
Intel-IOMMU.txt
intel_txt.txt
io-mapping.txt
io_ordering.txt
iostats.txt	block: Track DISCARD statistics and output them in stat and diskstat	2018-07-18 08:44:22 -06:00
IPMI.txt
IRQ-affinity.txt
IRQ-domain.txt
IRQ.txt
irqflags-tracing.txt
isa.txt
isapnp.txt
kernel-per-CPU-kthreads.txt
kobject.txt
kprobes.txt	kprobes/Documentation: Fix various typos	2018-06-22 11:10:55 +02:00
kref.txt
ldm.txt
lockup-watchdogs.txt
logo.gif
logo.txt
lsm.txt
lzo.txt
mailbox.txt
Makefile
memory-barriers.txt	sched/Documentation: Update wake_up() & co. memory-barrier guarantees	2018-07-17 09:30:34 +02:00
memory-hotplug.txt
men-chameleon-bus.txt
nommu-mmap.txt	Documentation: nommu-map: Fix duplicate word typo	2018-06-26 09:01:27 -06:00
ntb.txt
numastat.txt
padata.txt
parport-lowlevel.txt
percpu-rw-semaphore.txt
phy.txt
pi-futex.txt
pnp.txt
preempt-locking.txt
pwm.txt
rbtree.txt
remoteproc.txt
rfkill.txt	rfkill: Fix several typos in documentation	2018-06-15 13:36:08 +02:00
robust-futex-ABI.txt
robust-futexes.txt	futex: Update comments and docs about return values of arch futex code	2019-07-03 13:14:49 +02:00
rpmsg.txt
rtc.txt
SAK.txt
sgi-ioc4.txt
siphash.txt
SM501.txt
smsc_ece1099.txt
speculation.txt
static-keys.txt
SubmittingPatches
svga.txt
switchtec.txt
sync_file.txt
tee.txt
this_cpu_ops.txt
unaligned-memory-access.txt
vfio-mediated-device.txt	vfio/mdev: Check globally for duplicate devices	2018-06-08 10:24:27 -06:00
vfio.txt
video-output.txt
xillybus.txt
xz.txt
zorro.txt