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SubjectRe: perf: WARNING perfevents: irq loop stuck!

* Ingo Molnar <mingo@kernel.org> wrote:

>
> * Vince Weaver <vincent.weaver@maine.edu> wrote:
>
> > So this is just a warning, and I've reported it before, but the
> > perf_fuzzer triggers this fairly regularly on my Haswell system.
> >
> > It looks like fixed counter 0 (retired instructions) being set to
> > 0000fffffffffffe occasionally causes an irq loop storm and gets
> > stuck until the PMU state is cleared.
>
> So 0000fffffffffffe corresponds to 2 events left until overflow,
> right? And on Haswell we don't set x86_pmu.limit_period AFAICS, so we
> allow these super short periods.
>
> Maybe like on Broadwell we need a quirk on Nehalem/Haswell as well,
> one similar to bdw_limit_period()? Something like the patch below?
>
> Totally untested and such. I picked 128 because of Broadwell, but
> lower values might work as well. You could try to increase it to 3 and
> upwards and see which one stops triggering stuck NMI loops?
>
> Thanks,
>
> Ingo
>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>
> ---
> arch/x86/kernel/cpu/perf_event_intel.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> index 960e85de13fb..26b13ea8299c 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -2479,6 +2479,15 @@ hsw_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>
> return c;
> }
> +/*
> + * Really short periods might create infinite PMC NMI loops on Haswell,
> + * so limit them to 128. There's no official erratum for this AFAIK.
> + */
> +static unsigned int hsw_limit_period(struct perf_event *event, unsigned int left)
> +{
> + return max(left, 128U);
> +}
> +
>
> /*
> * Broadwell:
> @@ -2495,7 +2504,7 @@ hsw_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
> * Therefore the effective (average) period matches the requested period,
> * despite coarser hardware granularity.
> */
> -static unsigned bdw_limit_period(struct perf_event *event, unsigned left)
> +static unsigned int bdw_limit_period(struct perf_event *event, unsigned left)
> {
> if ((event->hw.config & INTEL_ARCH_EVENT_MASK) ==
> X86_CONFIG(.event=0xc0, .umask=0x01)) {
> @@ -3265,6 +3274,7 @@ __init int intel_pmu_init(void)
> x86_pmu.hw_config = hsw_hw_config;
> x86_pmu.get_event_constraints = hsw_get_event_constraints;
> x86_pmu.cpu_events = hsw_events_attrs;
> + x86_pmu.limit_period = hsw_limit_period;
> x86_pmu.lbr_double_abort = true;
> pr_cont("Haswell events, ");
> break;

Also, I'd apply the quirk not just to Haswell, but Nehalem, Westmere
and Ivy Bridge as well, I have seen it as early as on a Nehalem
prototype box.

Thanks,

Ingo


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