Re: [PATCH] perf/core: Fix account interrupt throttle

[Yang Jihong]

Hello,

Ping again, please take time to review, thanks.


Thanks,
Yang

On 2023/1/28 9:28, Yang Jihong wrote:
> Hello,
>
> PING
>
> Thanks,
> Yang
>
> On 2023/1/12 11:38, Yang Jihong wrote:
> > 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).
> >
> > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> > ---
> >   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 d56328e5080e..ced98e028d86 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -9414,7 +9414,7 @@ __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;
>
> .