Commit 0f0b7e1c authored by Juri Lelli's avatar Juri Lelli Committed by Thomas Gleixner
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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: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarThomas 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
parent 9e98c678

Documentation/admin-guide/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/tsc.c

+4 −1
Original line number Diff line number Diff line
@@ -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))

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