Commit 0051293c authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Reported-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Acked-by: default avatarWaiman Long <longman@redhat.com>
parent efc8b329

Documentation/admin-guide/kernel-parameters.txt

+6 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/tsc.c

+16 −2
Original line number Diff line number Diff line
@@ -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)