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| author | Venki Pallipadi <venkatesh.pallipadi@intel.com> | 2008-11-17 14:43:58 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-11-18 00:15:02 +0100 |
| commit | 93ce99e849433ede4ce8b410b749dc0cad1100b2 (patch) | |
| tree | 0481209f97a05a3851f536b2e16bd2868f83d842 /arch/x86/kernel/tsc_sync.c | |
| parent | 26a3e99160cfb06a0a33e25b9fb0d516e2cc680d (diff) | |
| download | linux-93ce99e849433ede4ce8b410b749dc0cad1100b2.tar.bz2 | |
x86: add rdtsc barrier to TSC sync check
Impact: fix incorrectly marked unstable TSC clock
Patch (commit 0d12cdd "sched: improve sched_clock() performance") has
a regression on one of the test systems here.
With the patch, I see:
checking TSC synchronization [CPU#0 -> CPU#1]:
Measured 28 cycles TSC warp between CPUs, turning off TSC clock.
Marking TSC unstable due to check_tsc_sync_source failed
Whereas, without the patch syncs pass fine on all CPUs:
checking TSC synchronization [CPU#0 -> CPU#1]: passed.
Due to this, TSC is marked unstable, when it is not actually unstable.
This is because syncs in check_tsc_wrap() goes away due to this commit.
As per the discussion on this thread, correct way to fix this is to add
explicit syncs as below?
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/kernel/tsc_sync.c')
| -rw-r--r-- | arch/x86/kernel/tsc_sync.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 9ffb01c31c40..1c0dfbca87c1 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -46,7 +46,9 @@ static __cpuinit void check_tsc_warp(void) cycles_t start, now, prev, end; int i; + rdtsc_barrier(); start = get_cycles(); + rdtsc_barrier(); /* * The measurement runs for 20 msecs: */ @@ -61,7 +63,9 @@ static __cpuinit void check_tsc_warp(void) */ __raw_spin_lock(&sync_lock); prev = last_tsc; + rdtsc_barrier(); now = get_cycles(); + rdtsc_barrier(); last_tsc = now; __raw_spin_unlock(&sync_lock); |