[patch] x86, tsc: skip TSC synchronization checks for tsc=reliable

Suresh Siddha
2011-11-04T22:39:29Z

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: Suresh Siddha <suresh.b.siddha@intel.com>
---
arch/x86/include/asm/tsc.h | 2 ++
arch/x86/kernel/tsc.c | 2 +-
arch/x86/kernel/tsc_sync.c | 4 ++--
3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 83e2efd..15d9915 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -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:
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index db48336..eee4651 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -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.
*/
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index 0aa5fed8..9eba29b 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -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;

/*