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x86/tsc: Add option to disable tsc clocksource watchdog 

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 <juri.lelli@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bigeasy@linutronix.de
Cc: linux-rt-users@vger.kernel.org
Cc: peterz@infradead.org
Cc: bristot@redhat.com
Cc: williams@redhat.com
Link: https://lkml.kernel.org/r/20190307120913.13168-1-juri.lelli@redhat.com
This commit is contained in:
Juri Lelli 2019-03-07 13:09:13 +01:00 committed by Thomas Gleixner
parent 9e98c678c2
commit 0f0b7e1cc7
2 changed files with 8 additions and 1 deletions
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4
Documentation/admin-guide/kernel-parameters.txt
View File

@ -4703,6 +4703,10 @@
[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

5
arch/x86/kernel/tsc.c
View File

@ -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;
}
@ -1349,7 +1352,7 @@ 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))