6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Qing Wang wangqing7171@gmail.com
[ Upstream commit f51972e6f8b9a737b2b3eb588069acb538fa72de ]
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 wangqing7171@gmail.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20250405141635.243786-3-wangqing7171@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 5dd6424e62fa8..6460f79280ed2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9553,14 +9553,14 @@ __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) {