From f51972e6f8b9a737b2b3eb588069acb538fa72de Mon Sep 17 00:00:00 2001 From: Qing Wang Date: Sat, 5 Apr 2025 22:16:35 +0800 Subject: [PATCH] perf/core: Fix broken throttling when max_samples_per_tick=1 According to the throttling mechanism, the pmu interrupts number can not exceed the max_samples_per_tick in one tick. But this mechanism is ineffective when max_samples_per_tick=1, because the throttling check is skipped during the first interrupt and only performed when the second interrupt arrives. Perhaps this bug may cause little influence in one tick, but if in a larger time scale, the problem can not be underestimated. When max_samples_per_tick = 1: Allowed-interrupts-per-second max-samples-per-second default-HZ ARCH 200 100 100 X86 500 250 250 ARM64 ... Obviously, the pmu interrupt number far exceed the user's expect. Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling") Signed-off-by: Qing Wang Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20250405141635.243786-3-wangqing7171@gmail.com --- kernel/events/core.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 3c69a1a3f41c2..05136e835042f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10065,14 +10065,14 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle) hwc->interrupts = 1; } else { hwc->interrupts++; - if (unlikely(throttle && - hwc->interrupts > max_samples_per_tick)) { - __this_cpu_inc(perf_throttled_count); - tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS); - hwc->interrupts = MAX_INTERRUPTS; - perf_log_throttle(event, 0); - ret = 1; - } + } + + if (unlikely(throttle && hwc->interrupts >= max_samples_per_tick)) { + __this_cpu_inc(perf_throttled_count); + tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS); + hwc->interrupts = MAX_INTERRUPTS; + perf_log_throttle(event, 0); + ret = 1; } if (event->attr.freq) { -- 2.47.2