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SubjectRe: [PATCH] perf/core: Fix endless multiplex timer
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On 3/5/2020 7:38 AM, Peter Zijlstra wrote:
> On Wed, Mar 04, 2020 at 09:20:42AM -0500, Liang, Kan wrote:
>>
>> NMI watchdog is pinned event.
>> ctx_event_to_rotate() will only pick an event from the flexible_groups.
>> So the cpu_ctx_sched_out() in perf_rotate_context() will never be called.
>
> Surely that's fixable; same principle.
>

Yes, after applying this patch, the issue has gone.

Tested-by: Kan Liang <kan.liang@linux.intel.com>

Thanks,
Kan
> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 3f1f77de7247..595fb3decd43 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2182,6 +2182,7 @@ __perf_remove_from_context(struct perf_event *event,
>
> if (!ctx->nr_events && ctx->is_active) {
> ctx->is_active = 0;
> + ctx->rotate_necessary = 0;
> if (ctx->task) {
> WARN_ON_ONCE(cpuctx->task_ctx != ctx);
> cpuctx->task_ctx = NULL;
> @@ -3077,12 +3078,6 @@ static void ctx_sched_out(struct perf_event_context *ctx,
> if (!ctx->nr_active || !(is_active & EVENT_ALL))
> return;
>
> - /*
> - * If we had been multiplexing, no rotations are necessary, now no events
> - * are active.
> - */
> - ctx->rotate_necessary = 0;
> -
> perf_pmu_disable(ctx->pmu);
> if (is_active & EVENT_PINNED) {
> list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list)
> @@ -3092,6 +3087,13 @@ static void ctx_sched_out(struct perf_event_context *ctx,
> if (is_active & EVENT_FLEXIBLE) {
> list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list)
> group_sched_out(event, cpuctx, ctx);
> +
> + /*
> + * Since we cleared EVENT_FLEXIBLE, also clear
> + * rotate_necessary, is will be reset by
> + * ctx_flexible_sched_in() when needed.
> + */
> + ctx->rotate_necessary = 0;
> }
> perf_pmu_enable(ctx->pmu);
> }
> @@ -3841,6 +3843,12 @@ ctx_event_to_rotate(struct perf_event_context *ctx)
> typeof(*event), group_node);
> }
>
> + /*
> + * Unconditionally clear rotate_necessary; if ctx_flexible_sched_in()
> + * finds there are unschedulable events, it will set it again.
> + */
> + ctx->rotate_necessary = 0;
> +
> return event;
> }
>
>

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