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

* [patch] x86, tsc: skip TSC synchronization checks for tsc=reliable
@ 2011-11-04 22:42 Suresh Siddha
  2011-11-07 18:06 ` john stultz
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Suresh Siddha @ 2011-11-04 22:42 UTC (permalink / raw)
  To: Thomas Gleixner, H Peter Anvin, Ingo Molnar, john stultz; +Cc: linux-kernel

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;
 
 	/*



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