Messages in this thread | | | Subject | Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle | From | Yang Jihong <> | Date | Fri, 14 Apr 2023 15:04:11 +0800 |
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Hello,
PING again. Look forward the review.
Thanks, Yang.
On 2023/3/22 15:36, Yang Jihong wrote: > Hello, > > PING. > > This patch has not been responded. > Please take time to check whether the fix solution is OK. > Look forward to reviewing the patch. Thanks :) > > Thanks, > Yang. > > On 2023/3/6 9:14, Yang Jihong wrote: >> Hello, >> >> PING. >> >> Thanks, >> Yang. >> >> On 2023/2/27 10:35, Yang Jihong wrote: >>> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling") >>> introduces a change in throttling threshold judgment. Before this, >>> compare hwc->interrupts and max_samples_per_tick, then increase >>> hwc->interrupts by 1, but this commit reverses order of these two >>> behaviors, causing the semantics of max_samples_per_tick to change. >>> In literal sense of "max_samples_per_tick", if hwc->interrupts == >>> max_samples_per_tick, it should not be throttled, therefore, the >>> judgment >>> condition should be changed to "hwc->interrupts > max_samples_per_tick". >>> >>> In fact, this may cause the hardlockup to fail, The minimum value of >>> max_samples_per_tick may be 1, in this case, the return value of >>> __perf_event_account_interrupt function is 1. >>> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86 >>> architecture as an example, see x86_pmu_handle_irq). >>> >>> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling") >>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com> >>> --- >>> >>> Changes since v2: >>> - Add fixed commit. >>> >>> Changes since v1: >>> - Modify commit title. >>> >>> kernel/events/core.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/kernel/events/core.c b/kernel/events/core.c >>> index f79fd8b87f75..0540a8653906 100644 >>> --- a/kernel/events/core.c >>> +++ b/kernel/events/core.c >>> @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct >>> perf_event *event, int throttle) >>> } else { >>> hwc->interrupts++; >>> if (unlikely(throttle >>> - && hwc->interrupts >= max_samples_per_tick)) { >>> + && 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; >>> >> >> . > > .
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