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Feng Tang 2fc7748d48 clocksource: Suspend the watchdog temporarily when high read latency detected 
[ Upstream commit b7082cdfc4 ]

Bugs have been reported on 8 sockets x86 machines in which the TSC was
wrongly disabled when the system is under heavy workload.

 [ 818.380354] clocksource: timekeeping watchdog on CPU336: hpet wd-wd read-back delay of 1203520ns
 [ 818.436160] clocksource: wd-tsc-wd read-back delay of 181880ns, clock-skew test skipped!
 [ 819.402962] clocksource: timekeeping watchdog on CPU338: hpet wd-wd read-back delay of 324000ns
 [ 819.448036] clocksource: wd-tsc-wd read-back delay of 337240ns, clock-skew test skipped!
 [ 819.880863] clocksource: timekeeping watchdog on CPU339: hpet read-back delay of 150280ns, attempt 3, marking unstable
 [ 819.936243] tsc: Marking TSC unstable due to clocksource watchdog
 [ 820.068173] TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.
 [ 820.092382] sched_clock: Marking unstable (818769414384, 1195404998)
 [ 820.643627] clocksource: Checking clocksource tsc synchronization from CPU 267 to CPUs 0,4,25,70,126,430,557,564.
 [ 821.067990] clocksource: Switched to clocksource hpet

This can be reproduced by running memory intensive 'stream' tests,
or some of the stress-ng subcases such as 'ioport'.

The reason for these issues is the when system is under heavy load, the
read latency of the clocksources can be very high.  Even lightweight TSC
reads can show high latencies, and latencies are much worse for external
clocksources such as HPET or the APIC PM timer.  These latencies can
result in false-positive clocksource-unstable determinations.

These issues were initially reported by a customer running on a production
system, and this problem was reproduced on several generations of Xeon
servers, especially when running the stress-ng test.  These Xeon servers
were not production systems, but they did have the latest steppings
and firmware.

Given that the clocksource watchdog is a continual diagnostic check with
frequency of twice a second, there is no need to rush it when the system
is under heavy load.  Therefore, when high clocksource read latencies
are detected, suspend the watchdog timer for 5 minutes.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Acked-by: Waiman Long <longman@redhat.com>
Cc: John Stultz <jstultz@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Feng Tang <feng.tang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-03-11 16:39:50 +01:00
arch x86/bugs: Reset speculation control settings on init 2023-03-11 16:39:49 +01:00
block blk-iocost: fix divide by 0 error in calc_lcoefs() 2023-03-11 16:39:48 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:13:17 +02:00
crypto crypto: rsa-pkcs1pad - Use akcipher_request_complete 2023-03-11 16:39:27 +01:00
Documentation ASoC: dt-bindings: meson: fix gx-card codec node regex 2023-03-11 16:39:36 +01:00
drivers ACPI: Don't build ACPICA with '-Os' 2023-03-11 16:39:50 +01:00
fs udf: Define EFSCORRUPTED error code 2023-03-11 16:39:48 +01:00
include rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks 2023-03-11 16:39:48 +01:00
init init/Kconfig: fix CC_HAS_ASM_GOTO_TIED_OUTPUT test with dash 2022-12-02 17:40:03 +01:00
io_uring io_uring: ensure that io_init_req() passes in the right issue_flags 2023-03-03 15:13:15 +01:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:24:00 +01:00
kernel clocksource: Suspend the watchdog temporarily when high read latency detected 2023-03-11 16:39:50 +01:00
lib printf: fix errname.c list 2023-03-11 16:39:40 +01:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm Revert "mm: Always release pages to the buddy allocator in memblock_free_late()." 2023-02-22 12:55:56 +01:00
net inet: fix fast path in __inet_hash_connect() 2023-03-11 16:39:50 +01:00
samples samples: vfio-mdev: Fix missing pci_disable_device() in mdpy_fb_probe() 2023-01-14 10:16:01 +01:00
scripts builddeb: clean generated package content 2023-03-11 16:39:46 +01:00
security tomoyo: fix broken dependency on *.conf.default 2023-02-01 08:23:10 +01:00
sound ASoC: tlv320adcx140: fix 'ti,gpio-config' DT property init 2023-03-11 16:39:38 +01:00
tools objtool: add UACCESS exceptions for __tsan_volatile_read/write 2023-03-11 16:39:41 +01:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:25:48 +01:00
virt kvm: Add support for arch compat vm ioctls 2022-10-30 09:41:15 +01:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
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 audit: update the mailing list in MAINTAINERS 2023-02-25 11:55:04 +01:00
Makefile Linux 5.10.172 2023-03-03 15:13:15 +01:00
README

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.