kernel/linux.git/drivers/clocksource/acpi_pm.c, branch v7.1

clocksource: Rewrite watchdog code completely

2026-03-20T12:36:32+00:00

The clocksource watchdog code has over time reached the state of an impenetrable maze of duct tape and staples. The original design, which was made in the context of systems far smaller than today, is based on the assumption that the to be monitored clocksource (TSC) can be trivially compared against a known to be stable clocksource (HPET/ACPI-PM timer). Over the years it turned out that this approach has major flaws: - Long delays between watchdog invocations can result in wrap arounds of the reference clocksource - Scalability of the reference clocksource readout can degrade on large multi-socket systems due to interconnect congestion This was addressed with various heuristics which degraded the accuracy of the watchdog to the point that it fails to detect actual TSC problems on older hardware which exposes slow inter CPU drifts due to firmware manipulating the TSC to hide SMI time. To address this and bring back sanity to the watchdog, rewrite the code completely with a different approach: 1) Restrict the validation against a reference clocksource to the boot CPU, which is usually the CPU/Socket closest to the legacy block which contains the reference source (HPET/ACPI-PM timer). Validate that the reference readout is within a bound latency so that the actual comparison against the TSC stays within 500ppm as long as the clocks are stable. 2) Compare the TSCs of the other CPUs in a round robin fashion against the boot CPU in the same way the TSC synchronization on CPU hotplug works. This still can suffer from delayed reaction of the remote CPU to the SMP function call and the latency of the control variable cache line. But this latency is not affecting correctness. It only affects the accuracy. With low contention the readout latency is in the low nanoseconds range, which detects even slight skews between CPUs. Under high contention this becomes obviously less accurate, but still detects slow skews reliably as it solely relies on subsequent readouts being monotonically increasing. It just can take slightly longer to detect the issue. 3) Rewrite the watchdog test so it tests the various mechanisms one by one and validating the result against the expectation. Signed-off-by: Thomas Gleixner Tested-by: Borislav Petkov (AMD) Tested-by: Daniel J Blueman Reviewed-by: Jiri Wiesner Reviewed-by: Daniel J Blueman Link: https://patch.msgid.link/20260123231521.926490888@kernel.org Link: https://patch.msgid.link/87h5qeomm5.ffs@tglx

clocksource: acpi_pm: Add external callback for suspend/resume

2024-09-06T12:49:20+00:00

Provides the capability to register an external callback for the ACPI PM timer, which is called during the suspend and resume processes. Signed-off-by: Marek Maslanka Reviewed-by: Hans de Goede Link: https://lore.kernel.org/r/20240812184150.1079924-1-mmaslanka@google.com Signed-off-by: Daniel Lezcano

clocksource: Verify HPET and PMTMR when TSC unverified

2023-02-02T22:23:02+00:00

On systems with two or fewer sockets, when the boot CPU has CONSTANT_TSC, NONSTOP_TSC, and TSC_ADJUST, clocksource watchdog verification of the TSC is disabled. This works well much of the time, but there is the occasional production-level system that meets all of these criteria, but which still has a TSC that skews significantly from atomic-clock time. This is usually attributed to a firmware or hardware fault. Yes, the various NTP daemons do express their opinions of userspace-to-atomic-clock time skew, but they put them in various places, depending on the daemon and distro in question. It would therefore be good for the kernel to have some clue that there is a problem. The old behavior of marking the TSC unstable is a non-starter because a great many workloads simply cannot tolerate the overheads and latencies of the various non-TSC clocksources. In addition, NTP-corrected systems sometimes can tolerate significant kernel-space time skew as long as the userspace time sources are within epsilon of atomic-clock time. Therefore, when watchdog verification of TSC is disabled, enable it for HPET and PMTMR (AKA ACPI PM timer). This provides the needed in-kernel time-skew diagnostic without degrading the system's performance. Signed-off-by: Paul E. McKenney Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Daniel Lezcano Cc: Waiman Long Cc: Tested-by: Feng Tang

clocksource: acpi_pm: fix return value of __setup handler

2022-03-18T13:59:27+00:00

__setup() handlers should return 1 to obsolete_checksetup() in init/main.c to indicate that the boot option has been handled. A return of 0 causes the boot option/value to be listed as an Unknown kernel parameter and added to init's (limited) environment strings. The __setup() handler interface isn't meant to handle negative return values -- they are non-zero, so they mean "handled" (like a return value of 1 does), but that's just a quirk. So return 1 from parse_pmtmr(). Also print a warning message if kstrtouint() returns an error. Fixes: 6b148507d3d0 ("pmtmr: allow command line override of ioport") Signed-off-by: Randy Dunlap Reported-by: Igor Zhbanov Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru Signed-off-by: Rafael J. Wysocki

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 243

2019-06-19T15:09:07+00:00

Based on 1 normalized pattern(s): this file is licensed under the gpl v2 extracted by the scancode license scanner the SPDX license identifier GPL-2.0-only has been chosen to replace the boilerplate/reference in 3 file(s). Signed-off-by: Thomas Gleixner Reviewed-by: Alexios Zavras Reviewed-by: Allison Randal Reviewed-by: Armijn Hemel Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190602204654.634736654@linutronix.de Signed-off-by: Greg Kroah-Hartman

clocksource: Use a plain u64 instead of cycle_t

2016-12-25T10:04:12+00:00

There is no point in having an extra type for extra confusion. u64 is unambiguous. Conversion was done with the following coccinelle script: @rem@ @@ -typedef u64 cycle_t; @fix@ typedef cycle_t; @@ -cycle_t +u64 Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: John Stultz

clocksource/drivers/acpi_pm: Convert to pr_* macros

2015-12-29T11:52:57+00:00

Like it's already done in one place in the driver, convert the rest to use pr_* macros instead of printk(KERN_LEVEL) calls. While here, join strings to be one string for one line to make grep on them easier. There is no functional change. Signed-off-by: Andy Shevchenko Cc: Daniel Lezcano Link: http://lkml.kernel.org/r/1451310085-113182-1-git-send-email-andriy.shevchenko@linux.intel.com Signed-off-by: Thomas Gleixner

treewide: Fix printks with 0x%#

2013-08-27T08:49:38+00:00

Using 0x%# emits 0x0x. Only one is necessary. Signed-off-by: Joe Perches Acked-by: Takashi Iwai Signed-off-by: Jiri Kosina

Drivers: clocksource: remove __dev* attributes.

2013-01-03T23:57:15+00:00

CONFIG_HOTPLUG is going away as an option. As a result, the __dev* markings need to be removed. This change removes the use of __devinit, __devexit_p, __devinitdata, __devinitconst, and __devexit from these drivers. Based on patches originally written by Bill Pemberton, but redone by me in order to handle some of the coding style issues better, by hand. Cc: Bill Pemberton Cc: John Stultz Cc: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

clocksource: clean up parse_pmtmr()

2012-11-13T19:04:50+00:00

I changed the strict_strtoul() to kstrtouint(). That has the check for UINT_MAX built in to it so the ifdefs can be removed. Also I changed a printk() to pr_info(). Signed-off-by: Dan Carpenter Signed-off-by: John Stultz