diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index cdcebf30468a..cdb19e3ba3aa 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -3952,6 +3952,85 @@ static inline bool intel_pmu_has_cap(struct perf_event *event, int idx) return test_bit(idx, (unsigned long *)&intel_cap->capabilities); } +static u64 intel_pmu_freq_start_period(struct perf_event *event) +{ + int type = event->attr.type; + u64 config, factor; + s64 start; + + /* + * The 127 is the lowest possible recommended SAV (sample after value) + * for a 4000 freq (default freq), according to the event list JSON file. + * Also, assume the workload is idle 50% time. + */ + factor = 64 * 4000; + if (type != PERF_TYPE_HARDWARE && type != PERF_TYPE_HW_CACHE) + goto end; + + /* + * The estimation of the start period in the freq mode is + * based on the below assumption. + * + * For a cycles or an instructions event, 1GHZ of the + * underlying platform, 1 IPC. The workload is idle 50% time. + * The start period = 1,000,000,000 * 1 / freq / 2. + * = 500,000,000 / freq + * + * Usually, the branch-related events occur less than the + * instructions event. According to the Intel event list JSON + * file, the SAV (sample after value) of a branch-related event + * is usually 1/4 of an instruction event. + * The start period of branch-related events = 125,000,000 / freq. + * + * The cache-related events occurs even less. The SAV is usually + * 1/20 of an instruction event. + * The start period of cache-related events = 25,000,000 / freq. + */ + config = event->attr.config & PERF_HW_EVENT_MASK; + if (type == PERF_TYPE_HARDWARE) { + switch (config) { + case PERF_COUNT_HW_CPU_CYCLES: + case PERF_COUNT_HW_INSTRUCTIONS: + case PERF_COUNT_HW_BUS_CYCLES: + case PERF_COUNT_HW_STALLED_CYCLES_FRONTEND: + case PERF_COUNT_HW_STALLED_CYCLES_BACKEND: + case PERF_COUNT_HW_REF_CPU_CYCLES: + factor = 500000000; + break; + case PERF_COUNT_HW_BRANCH_INSTRUCTIONS: + case PERF_COUNT_HW_BRANCH_MISSES: + factor = 125000000; + break; + case PERF_COUNT_HW_CACHE_REFERENCES: + case PERF_COUNT_HW_CACHE_MISSES: + factor = 25000000; + break; + default: + goto end; + } + } + + if (type == PERF_TYPE_HW_CACHE) + factor = 25000000; +end: + /* + * Usually, a prime or a number with less factors (close to prime) + * is chosen as an SAV, which makes it less likely that the sampling + * period synchronizes with some periodic event in the workload. + * Minus 1 to make it at least avoiding values near power of twos + * for the default freq. + */ + start = DIV_ROUND_UP_ULL(factor, event->attr.sample_freq) - 1; + + if (start > x86_pmu.max_period) + start = x86_pmu.max_period; + + if (x86_pmu.limit_period) + x86_pmu.limit_period(event, &start); + + return start; +} + static int intel_pmu_hw_config(struct perf_event *event) { int ret = x86_pmu_hw_config(event); @@ -3963,6 +4042,12 @@ static int intel_pmu_hw_config(struct perf_event *event) if (ret) return ret; + if (event->attr.freq && event->attr.sample_freq) { + event->hw.sample_period = intel_pmu_freq_start_period(event); + event->hw.last_period = event->hw.sample_period; + local64_set(&event->hw.period_left, event->hw.sample_period); + } + if (event->attr.precise_ip) { if ((event->attr.config & INTEL_ARCH_EVENT_MASK) == INTEL_FIXED_VLBR_EVENT) return -EINVAL;