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Commit 28a00184 authored by Suresh Siddha's avatar Suresh Siddha Committed by Ingo Molnar
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x86, tsc: Skip TSC synchronization checks for tsc=reliable 



tsc=reliable boot parameter is supposed to skip all the TSC
stablility checks during boot time.

On a 8-socket system where we want to run an experiment with the
"tsc=reliable" boot option, TSC synchronization checks are not
getting skipped and marking the TSC as not stable.

Check for tsc_clocksource_reliable (which is set via
tsc=reliable or for platforms supporting synthetic TSC_RELIABLE
feature bit etc) and when set, skip the TSC synchronization
tests during boot.

Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Acked-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Tested-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1320446537.15071.14.camel@sbsiddha-desk.sc.intel.com


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 8e8da023

arch/x86/include/asm/tsc.h

+2 −0
Original line number Diff line number Diff line
@@ -51,6 +51,8 @@ extern int unsynchronized_tsc(void); 
extern int check_tsc_unstable(void);

extern unsigned long native_calibrate_tsc(void);



extern int tsc_clocksource_reliable;



/*

 * Boot-time check whether the TSCs are synchronized across

 * all CPUs/cores:

arch/x86/kernel/tsc.c

+1 −1
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ static int __read_mostly tsc_unstable; 
   erroneous rdtsc usage on !cpu_has_tsc processors */

static int __read_mostly tsc_disabled = -1;



static int tsc_clocksource_reliable;

int tsc_clocksource_reliable;

/*

 * Scheduler clock - returns current time in nanosec units.

 */

arch/x86/kernel/tsc_sync.c

+2 −2
Original line number Diff line number Diff line
@@ -113,7 +113,7 @@ void __cpuinit check_tsc_sync_source(int cpu) 
	if (unsynchronized_tsc())

		return;



	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {

	if (tsc_clocksource_reliable) {

		if (cpu == (nr_cpu_ids-1) || system_state != SYSTEM_BOOTING)

			pr_info(

			"Skipped synchronization checks as TSC is reliable.\n");
@@ -172,7 +172,7 @@ void __cpuinit check_tsc_sync_target(void) 
{

	int cpus = 2;



	if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE))

	if (unsynchronized_tsc() || tsc_clocksource_reliable)

		return;



	/*