Paul E. McKenney dba9cda5aa clocksource: Retry clock read if long delays detected ... [ Upstream commit db3a34e17433de2390eb80d436970edcebd0ca3e ] 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>		2021-07-14 16:53:18 +02:00
..
ABI	evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded	2021-07-14 16:53:08 +02:00
EDID	docs: driver-api: add a series of orphaned documents	2019-07-15 11:03:02 -03:00
PCI	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2019-08-27 14:23:31 -07:00
RCU	Merge branches 'consolidate.2019.08.01b', 'fixes.2019.08.12a', 'lists.2019.08.13a' and 'torture.2019.08.01b' into HEAD	2019-08-13 14:30:30 -07:00
accounting	docs: add some documentation dirs to the driver-api book	2019-07-15 11:03:02 -03:00
admin-guide	clocksource: Retry clock read if long delays detected	2021-07-14 16:53:18 +02:00
arm	ARM: 9012/1: move device tree mapping out of linear region	2021-05-19 10:08:32 +02:00
arm64	arm64: errata: Hide CTR_EL0.DIC on systems affected by Neoverse-N1 #1542419	2020-04-29 16:32:56 +02:00
block	docs: block: null_blk: enhance document style	2019-09-11 16:04:22 -06:00
bpf	bpf/flow_dissector: document flags	2019-07-25 18:00:41 -07:00
cdrom	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
core-api	XArray: add xas_split	2021-06-10 13:37:14 +02:00
cpu-freq	Documentation: cpufreq: Update policy notifier documentation	2019-09-02 22:44:05 +02:00
crypto	Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6	2019-09-18 12:11:14 -07:00
dev-tools	mm, page_owner: decouple freeing stack trace from debug_pagealloc	2019-10-14 15:04:00 -07:00
devicetree	dt-bindings: net: ethernet-controller: fix typo in NVMEM	2021-04-14 08:24:18 +02:00
doc-guide	docs: remove extra conf.py files	2019-07-17 06:57:52 -03:00
driver-api	ata: make qc_prep return ata_completion_errors	2020-10-01 13:18:26 +02:00
fault-injection	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
fb	fbdev: fix numbering of fbcon options	2020-02-24 08:36:42 +01:00
features	It's a somewhat calmer cycle for docs this time, as the churn of the mass	2019-09-17 16:22:26 -07:00
filesystems	sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output	2021-03-07 12:20:48 +01:00
firmware-guide	Documentation: ACPI: DSD: Convert LED documentation to ReST	2019-08-20 23:53:46 +02:00
firmware_class	…
fpga	Documentation: fpga: dfl: add descriptions for virtualization and new interfaces.	2019-09-03 19:35:42 -07:00
gpu	Merge drm/drm-next into drm-intel-next-queued	2019-08-22 00:10:36 -07:00
hid	docs: add some documentation dirs to the driver-api book	2019-07-15 11:03:02 -03:00
hwmon	hwmon: (max31790) Fix pwmX_enable attributes	2021-07-14 16:53:14 +02:00
i2c	docs: i2c: convert to ReST and add to driver-api bookset	2019-07-31 13:25:27 -06:00
ia64	docs: add SPDX tags to new index files	2019-07-15 11:03:03 -03:00
ide	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
iio	docs: add some documentation dirs to the driver-api book	2019-07-15 11:03:02 -03:00
infiniband	Documentation/infiniband: update name of some functions	2019-09-13 16:55:55 -03:00
input	Input: docs: fix spelling mistake "potocol" -> "protocol"	2019-08-06 11:24:49 -06:00
ioctl	fs-verity: add UAPI header	2019-07-28 16:59:16 -07:00
isdn	docs: isdn: convert to ReST and add to kAPI bookset	2019-07-31 13:30:25 -06:00
kbuild	kbuild: support LLVM=1 to switch the default tools to Clang/LLVM	2020-08-26 10:40:47 +02:00
kernel-hacking	docs: Add documentation for Symbol Namespaces	2019-09-10 10:30:49 +02:00
leds	leds: core: Add support for composing LED class device names	2019-07-25 20:07:52 +02:00
livepatch	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
locking	doc🔒 remove reference to clever use of read-write lock	2019-09-14 01:53:27 -06:00
m68k	docs: README.buddha: convert to ReST and add to m68k book	2019-07-31 13:30:10 -06:00
maintainer	docs: Fix typo on pull requests guide	2019-08-12 15:14:14 -06:00
media	media: videodev2.h: RGB BT2020 and HSV are always full range	2020-11-05 11:43:15 +01:00
mic	docs: driver-api: add remaining converted dirs to it	2019-07-15 11:03:03 -03:00
mips	Main MIPS changes for v5.4:	2019-09-22 09:30:30 -07:00
misc-devices	Docs: misc: xilinx_sdfec: Add documentation	2019-08-15 17:54:38 +02:00
netlabel	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
networking	can: j1939: swap addr and pgn in the send example	2020-11-18 19:20:19 +01:00
nios2	docs: nios2: add it to the main Documentation body	2019-07-31 13:31:51 -06:00
openrisc	docs: openrisc: convert to ReST and add to documentation body	2019-07-31 13:30:20 -06:00
parisc	docs: parisc: convert to ReST and add to documentation body	2019-07-31 13:30:15 -06:00
pcmcia	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
power	Merge branches 'pm-opp', 'pm-qos', 'acpi-pm', 'pm-domains' and 'pm-tools'	2019-09-17 09:49:19 +02:00
powerpc	docs: powerpc: Add missing documentation reference	2019-09-17 23:59:34 +10:00
process	Documentation/process: Add fallthrough pseudo-keyword	2019-10-11 09:26:05 -07:00
riscv	It's a somewhat calmer cycle for docs this time, as the churn of the mass	2019-09-17 16:22:26 -07:00
s390	Documentation/s390: remove outdated debugging390 documentation	2019-08-21 12:41:43 +02:00
scheduler	sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices	2019-08-08 09:09:30 +02:00
scsi	scsi: smartpqi: Update attribute name to `driver_version`	2020-01-17 19:48:27 +01:00
security	Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity	2019-09-27 19:37:27 -07:00
sh	docs: remove extra conf.py files	2019-07-17 06:57:52 -03:00
sound	ALSA: hda/realtek - Remove now-unnecessary XPS 13 headphone noise fixups	2020-04-17 10:50:08 +02:00
sparc	docs: add arch doc directories to the index	2019-07-15 11:03:01 -03:00
sphinx	tweewide: Fix most Shebang lines	2021-05-22 11:38:30 +02:00
sphinx-static	…
spi	spi: docs: convert to ReST and add it to the kABI bookset	2019-07-31 14:13:13 -06:00
target	tweewide: Fix most Shebang lines	2021-05-22 11:38:30 +02:00
timers	docs: add some directories to the main documentation index	2019-07-15 11:03:03 -03:00
trace	tweewide: Fix most Shebang lines	2021-05-22 11:38:30 +02:00
translations	doc: arm64: fix grammar dtb placed in no attributes region	2019-09-06 08:44:34 -06:00
usb	USB: rio500: Remove Rio 500 kernel driver	2019-10-04 10:53:36 +02:00
userspace-api	Documentation: seccomp: Fix user notification documentation	2021-06-03 08:59:03 +02:00
virt	KVM: arm64: Reject VM creation when the default IPA size is unsupported	2021-03-17 17:03:57 +01:00
virtual	cpuidle: add haltpoll governor	2019-07-30 17:27:37 +02:00
vm	mm/slub: clarify verification reporting	2021-06-23 14:41:30 +02:00
w1	docs: w1: convert to ReST and add to the kAPI group of docs	2019-07-31 14:16:17 -06:00
watchdog	linux-watchdog 5.4-rc1 tag	2019-09-27 11:17:38 -07:00
x86	x86/CPU/AMD: Save AMD NodeId as cpu_die_id	2020-12-30 11:51:47 +01:00
xtensa	xtensa: fix TLBTEMP area placement	2020-11-24 13:29:22 +01:00
.gitignore	…
COPYING-logo	docs: logo.txt: rename it to COPYING-logo	2019-07-15 09:20:27 -03:00
Changes	…
CodingStyle	…
DMA-API-HOWTO.txt	docs: DMA-API-HOWTO.txt: fix an unmarked code block	2019-07-15 09:20:24 -03:00
DMA-API.txt	dma-mapping: remove dma_release_declared_memory	2019-09-04 11:13:19 +02:00
DMA-ISA-LPC.txt	…
DMA-attributes.txt	…
IPMI.txt	…
IRQ-affinity.txt	…
IRQ-domain.txt	…
IRQ.txt	…
Kconfig	docs: Kbuild/Makefile: allow check for missing docs at build time	2019-06-07 11:33:16 -06:00
Makefile	docs: Kbuild/Makefile: allow check for missing docs at build time	2019-06-07 11:33:16 -06:00
SubmittingPatches	…
asm-annotations.rst	linkage: Introduce new macros for assembler symbols	2020-11-10 12:37:24 +01:00
atomic_bitops.txt	docs: atomic_bitops.txt: add a title for this document	2019-04-11 12:37:02 -06:00
atomic_t.txt	Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2019-07-08 16:12:03 -07:00
bus-virt-phys-mapping.txt	…
conf.py	docs: conf.py: only use CJK if the font is available	2019-07-17 06:57:51 -03:00
crc32.txt	…
debugging-modules.txt	…
debugging-via-ohci1394.txt	…
digsig.txt	…
docutils.conf	doc-rst: Add missing newline at end of file	2019-06-20 14:16:56 -06:00
dontdiff	kbuild: create *.mod with full directory path and remove MODVERDIR	2019-07-18 02:19:31 +09:00
futex-requeue-pi.txt	…
hwspinlock.txt	hwspinlock: add the 'in_atomic' API	2019-06-29 21:08:14 -07:00
index.rst	linkage: Introduce new macros for assembler symbols	2020-11-10 12:37:24 +01:00
io-mapping.txt	…
io_ordering.txt	…
irqflags-tracing.txt	…
kobject.txt	…
kprobes.txt	Merge branch 'parisc-5.2-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux	2019-05-07 19:34:17 -07:00
kref.txt	…
logo.gif	…
lzo.txt	lib/lzo: fix ambiguous encoding bug in lzo-rle	2020-06-17 16:40:28 +02:00
mailbox.txt	…
memory-barriers.txt	docs: fix broken doc references due to renames	2019-07-17 06:57:51 -03:00
nommu-mmap.txt	…
padata.txt	padata: allocate workqueue internally	2019-09-13 21:15:39 +10:00
percpu-rw-semaphore.txt	…
pi-futex.txt	docs: locking: convert docs to ReST and rename to *.rst	2019-07-15 08:53:27 -03:00
preempt-locking.txt	x86/fpu: Remove fpu__restore()	2019-04-09 19:27:42 +02:00
rbtree.txt	docs: rbtree.txt: fix Sphinx build warnings	2019-07-15 09:20:24 -03:00
remoteproc.txt	remoteproc: add vendor resources handling	2019-06-29 12:02:17 -07:00
robust-futex-ABI.txt	…
robust-futexes.txt	futex: Update comments and docs about return values of arch futex code	2019-04-26 13:57:55 +01:00
rpmsg.txt	…
speculation.txt	docs: speculation.txt: mark example blocks as such	2019-04-11 12:37:03 -06:00
static-keys.txt	…
tee.txt	Documentation: tee: Grammar s/the its/its/	2019-06-07 11:23:38 -06:00
this_cpu_ops.txt	…
unaligned-memory-access.txt	docs: unaligned-memory-access.txt: use a lowercase title	2019-04-11 12:37:03 -06:00
xz.txt	…