diff options
| -rw-r--r-- | arch/x86/kernel/tsc_sync.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 78083bf23ed1..40f8edd55151 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -37,6 +37,7 @@ static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED; static cycles_t last_tsc; static cycles_t max_warp; static int nr_warps; +static int random_warps; /* * TSC-warp measurement loop running on both CPUs. This is not called @@ -45,7 +46,7 @@ static int nr_warps; static void check_tsc_warp(unsigned int timeout) { cycles_t start, now, prev, end; - int i; + int i, cur_warps = 0; start = rdtsc_ordered(); /* @@ -85,7 +86,14 @@ static void check_tsc_warp(unsigned int timeout) if (unlikely(prev > now)) { arch_spin_lock(&sync_lock); max_warp = max(max_warp, prev - now); + /* + * Check whether this bounces back and forth. Only + * one CPU should observe time going backwards. + */ + if (cur_warps != nr_warps) + random_warps++; nr_warps++; + cur_warps = nr_warps; arch_spin_unlock(&sync_lock); } } @@ -160,6 +168,8 @@ void check_tsc_sync_source(int cpu) smp_processor_id(), cpu); pr_warning("Measured %Ld cycles TSC warp between CPUs, " "turning off TSC clock.\n", max_warp); + if (random_warps) + pr_warning("TSC warped randomly between CPUs\n"); mark_tsc_unstable("check_tsc_sync_source failed"); } else { pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", @@ -170,6 +180,7 @@ void check_tsc_sync_source(int cpu) * Reset it - just in case we boot another CPU later: */ atomic_set(&start_count, 0); + random_warps = 0; nr_warps = 0; max_warp = 0; last_tsc = 0; |