diff options
Diffstat (limited to 'arch/x86/kernel/tsc_sync.c')
| -rw-r--r-- | arch/x86/kernel/tsc_sync.c | 83 |
1 files changed, 78 insertions, 5 deletions
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 9ad074c87e72..d7f48a640ff5 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -149,6 +149,7 @@ bool tsc_store_and_check_tsc_adjust(void) static atomic_t start_count; static atomic_t stop_count; static atomic_t skip_test; +static atomic_t test_runs; /* * We use a raw spinlock in this exceptional case, because @@ -269,6 +270,16 @@ void check_tsc_sync_source(int cpu) } /* + * Set the maximum number of test runs to + * 1 if the CPU does not provide the TSC_ADJUST MSR + * 3 if the MSR is available, so the target can try to adjust + */ + if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST)) + atomic_set(&test_runs, 1); + else + atomic_set(&test_runs, 3); +retry: + /* * Wait for the target to start or to skip the test: */ while (atomic_read(&start_count) != cpus - 1) { @@ -289,7 +300,21 @@ void check_tsc_sync_source(int cpu) while (atomic_read(&stop_count) != cpus-1) cpu_relax(); - if (nr_warps) { + /* + * If the test was successful set the number of runs to zero and + * stop. If not, decrement the number of runs an check if we can + * retry. In case of random warps no retry is attempted. + */ + if (!nr_warps) { + atomic_set(&test_runs, 0); + + pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", + smp_processor_id(), cpu); + + } else if (atomic_dec_and_test(&test_runs) || random_warps) { + /* Force it to 0 if random warps brought us here */ + atomic_set(&test_runs, 0); + pr_warning("TSC synchronization [CPU#%d -> CPU#%d]:\n", smp_processor_id(), cpu); pr_warning("Measured %Ld cycles TSC warp between CPUs, " @@ -297,9 +322,6 @@ void check_tsc_sync_source(int cpu) 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", - smp_processor_id(), cpu); } /* @@ -315,6 +337,12 @@ void check_tsc_sync_source(int cpu) * Let the target continue with the bootup: */ atomic_inc(&stop_count); + + /* + * Retry, if there is a chance to do so. + */ + if (atomic_read(&test_runs) > 0) + goto retry; } /* @@ -322,6 +350,9 @@ void check_tsc_sync_source(int cpu) */ void check_tsc_sync_target(void) { + struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust); + unsigned int cpu = smp_processor_id(); + cycles_t cur_max_warp, gbl_max_warp; int cpus = 2; /* Also aborts if there is no TSC. */ @@ -337,6 +368,7 @@ void check_tsc_sync_target(void) return; } +retry: /* * Register this CPU's participation and wait for the * source CPU to start the measurement: @@ -345,7 +377,12 @@ void check_tsc_sync_target(void) while (atomic_read(&start_count) != cpus) cpu_relax(); - check_tsc_warp(loop_timeout(smp_processor_id())); + cur_max_warp = check_tsc_warp(loop_timeout(cpu)); + + /* + * Store the maximum observed warp value for a potential retry: + */ + gbl_max_warp = max_warp; /* * Ok, we are done: @@ -362,6 +399,42 @@ void check_tsc_sync_target(void) * Reset it for the next sync test: */ atomic_set(&stop_count, 0); + + /* + * Check the number of remaining test runs. If not zero, the test + * failed and a retry with adjusted TSC is possible. If zero the + * test was either successful or failed terminally. + */ + if (!atomic_read(&test_runs)) + return; + + /* + * If the warp value of this CPU is 0, then the other CPU + * observed time going backwards so this TSC was ahead and + * needs to move backwards. + */ + if (!cur_max_warp) + cur_max_warp = -gbl_max_warp; + + /* + * Add the result to the previous adjustment value. + * + * The adjustement value is slightly off by the overhead of the + * sync mechanism (observed values are ~200 TSC cycles), but this + * really depends on CPU, node distance and frequency. So + * compensating for this is hard to get right. Experiments show + * that the warp is not longer detectable when the observed warp + * value is used. In the worst case the adjustment needs to go + * through a 3rd run for fine tuning. + */ + cur->adjusted += cur_max_warp; + + pr_warn("TSC ADJUST compensate: CPU%u observed %lld warp. Adjust: %lld\n", + cpu, cur_max_warp, cur->adjusted); + + wrmsrl(MSR_IA32_TSC_ADJUST, cur->adjusted); + goto retry; + } #endif /* CONFIG_SMP */ |