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| author | Paul E. McKenney <paulmck@kernel.org> | 2023-02-01 13:53:07 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2023-02-06 16:38:30 -0800 |
| commit | 0051293c533017e2a860e0a0a33517bc40240fff (patch) | |
| tree | 54297a31350169661fd6f40446cf5f49025dd9bd | |
| parent | efc8b329c7fdc30921a7dfc109237523e1e5b1cc (diff) | |
| download | lwn-0051293c533017e2a860e0a0a33517bc40240fff.tar.gz lwn-0051293c533017e2a860e0a0a33517bc40240fff.zip | |
clocksource: Enable TSC watchdog checking of HPET and PMTMR only when requested
Unconditionally enabling TSC watchdog checking of the HPET and PMTMR
clocksources can degrade latency and performance. Therefore, provide
a new "watchdog" option to the tsc= boot parameter that opts into such
checking. Note that tsc=watchdog is overridden by a tsc=nowatchdog
regardless of their relative positions in the list of boot parameters.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Waiman Long <longman@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 6 | ||||
| -rw-r--r-- | arch/x86/kernel/tsc.c | 18 |
2 files changed, 22 insertions, 2 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 95f0d104c232..7b4df6d89d3c 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -6373,6 +6373,12 @@ (HPET or PM timer) on systems whose TSC frequency was obtained from HW or FW using either an MSR or CPUID(0x15). Warn if the difference is more than 500 ppm. + [x86] watchdog: Use TSC as the watchdog clocksource with + which to check other HW timers (HPET or PM timer), but + only on systems where TSC has been deemed trustworthy. + This will be suppressed by an earlier tsc=nowatchdog and + can be overridden by a later tsc=nowatchdog. A console + message will flag any such suppression or overriding. tsc_early_khz= [X86] Skip early TSC calibration and use the given value instead. Useful when the early TSC frequency discovery diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index a5371c6d4b64..306c233c98d8 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -294,6 +294,7 @@ __setup("notsc", notsc_setup); static int no_sched_irq_time; static int no_tsc_watchdog; +static int tsc_as_watchdog; static int __init tsc_setup(char *str) { @@ -303,10 +304,22 @@ static int __init tsc_setup(char *str) no_sched_irq_time = 1; if (!strcmp(str, "unstable")) mark_tsc_unstable("boot parameter"); - if (!strcmp(str, "nowatchdog")) + if (!strcmp(str, "nowatchdog")) { no_tsc_watchdog = 1; + if (tsc_as_watchdog) + pr_alert("%s: Overriding earlier tsc=watchdog with tsc=nowatchdog\n", + __func__); + tsc_as_watchdog = 0; + } if (!strcmp(str, "recalibrate")) tsc_force_recalibrate = 1; + if (!strcmp(str, "watchdog")) { + if (no_tsc_watchdog) + pr_alert("%s: tsc=watchdog overridden by earlier tsc=nowatchdog\n", + __func__); + else + tsc_as_watchdog = 1; + } return 1; } @@ -1192,7 +1205,8 @@ static void __init tsc_disable_clocksource_watchdog(void) bool tsc_clocksource_watchdog_disabled(void) { - return !(clocksource_tsc.flags & CLOCK_SOURCE_MUST_VERIFY); + return !(clocksource_tsc.flags & CLOCK_SOURCE_MUST_VERIFY) && + tsc_as_watchdog && !no_tsc_watchdog; } static void __init check_system_tsc_reliable(void) |