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authorPaul E. McKenney <paulmck@kernel.org>2022-12-21 16:20:25 -0800
committerPaul E. McKenney <paulmck@kernel.org>2023-02-02 14:23:02 -0800
commitefc8b329c7fdc30921a7dfc109237523e1e5b1cc (patch)
tree6cb2b1259422aacd521c2c217e262cc365fc9b19 /drivers/clocksource
parenta7ec817d55421ac214cac9d3e5ebb65d848198dc (diff)
clocksource: Verify HPET and PMTMR when TSC unverified
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 <paulmck@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Waiman Long <longman@redhat.com> Cc: <x86@kernel.org> Tested-by: Feng Tang <feng.tang@intel.com>
Diffstat (limited to 'drivers/clocksource')
-rw-r--r--drivers/clocksource/acpi_pm.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 279ddff81ab4..82338773602c 100644
--- a/drivers/clocksource/acpi_pm.c
+++ b/drivers/clocksource/acpi_pm.c
@@ -23,6 +23,7 @@
#include <linux/pci.h>
#include <linux/delay.h>
#include <asm/io.h>
+#include <asm/time.h>
/*
* The I/O port the PMTMR resides at.
@@ -210,8 +211,9 @@ static int __init init_acpi_pm_clocksource(void)
return -ENODEV;
}
- return clocksource_register_hz(&clocksource_acpi_pm,
- PMTMR_TICKS_PER_SEC);
+ if (tsc_clocksource_watchdog_disabled())
+ clocksource_acpi_pm.flags |= CLOCK_SOURCE_MUST_VERIFY;
+ return clocksource_register_hz(&clocksource_acpi_pm, PMTMR_TICKS_PER_SEC);
}
/* We use fs_initcall because we want the PCI fixups to have run