From 0051293c533017e2a860e0a0a33517bc40240fff Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 1 Feb 2023 13:53:07 -0800 Subject: [PATCH] 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 Reported-by: Waiman Long Signed-off-by: Paul E. McKenney Acked-by: Waiman Long --- Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ 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 95f0d10..7b4df6d 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 a5371c6..306c233 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) -- 2.7.4