Clocksource watchdog has been found responsible for generating latency spikes (in the 10-20 us range) when woken up to check for TSC stability.
Add an option to disable it at boot. Signed-off-by: Juri Lelli <[email protected]> --- Sending this out as an RFC after yesterday discussion with Thomas on IRC. AFAICT, CLOCK_SOURCE_MUST_VERIFY only controls enqueue\dequeue of the watchdog. TSC sync checks are still done if tsc_clocksource_reliable is set (booting w/o tsc=reliable). Thomas, is this anywhere close to what you had in mind? --- Documentation/admin-guide/kernel-parameters.txt | 4 ++++ arch/x86/kernel/tsc.c | 5 ++++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f5acf35c712f..ea7c4967aa80 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4619,6 +4619,10 @@ [x86] unstable: mark the TSC clocksource as unstable, this marks the TSC unconditionally unstable at bootup and avoids any further wobbles once the TSC watchdog notices. + [x86] nowatchdog: disable clocksource watchdog. Used + in situations with strict latency requirements (where + interruptions from clocksource watchdog are not + acceptable). turbografx.map[2|3]= [HW,JOY] TurboGraFX parallel port interface diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 6d5dc5dabfd7..4b753d057aee 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -283,6 +283,7 @@ int __init notsc_setup(char *str) __setup("notsc", notsc_setup); static int no_sched_irq_time; +static int no_tsc_watchdog; static int __init tsc_setup(char *str) { @@ -292,6 +293,8 @@ 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")) + no_tsc_watchdog = 1; return 1; } @@ -1347,7 +1350,7 @@ static int __init init_tsc_clocksource(void) if (tsc_unstable) goto unreg; - if (tsc_clocksource_reliable) + if (tsc_clocksource_reliable || no_tsc_watchdog) clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY; if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3)) -- 2.17.2
