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SubjectRe: [PATCH v3 1/3] perf: Allow using AUX data in perf samples
Date
Peter Zijlstra <peterz@infradead.org> writes:

> On Mon, Oct 28, 2019 at 05:27:12PM +0100, Peter Zijlstra wrote:
>> And while I get why we need recursion protection for pmu::snapshot_aux,
>> I'm a little puzzled on why it is over the padding, that is, why isn't
>> the whole of aux_in_sampling inside (the newly minted)
>> perf_pmu_snapshot_aux() ?
>
> That is, given the previous delta, the below.
>
> ---
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6292,9 +6292,17 @@ long perf_pmu_snapshot_aux(struct perf_e
> * IRQs need to be disabled to prevent IPIs from racing with us.
> */
> local_irq_save(flags);
> + /*
> + * Guard against NMI hits inside the critical section;
> + * see also perf_prepare_sample_aux().
> + */
> + WRITE_ONCE(rb->aux_in_sampling, 1);
> + barrier();
>
> ret = event->pmu->snapshot_aux(event, handle, size);
>
> + barrier();
> + WRITE_ONCE(rb->aux_in_sampling, 0);
> local_irq_restore(flags);
>
> return ret;
> @@ -6316,13 +6324,6 @@ static void perf_aux_sample_output(struc
> if (!rb)
> return;
>
> - /*
> - * Guard against NMI hits inside the critical section;
> - * see also perf_prepare_sample_aux().
> - */
> - WRITE_ONCE(rb->aux_in_sampling, 1);
> - barrier();
> -
> size = perf_pmu_snapshot_aux(sampler, handle, data->aux_size);
>
> /*
> @@ -6348,9 +6349,6 @@ static void perf_aux_sample_output(struc
> }
>
> out_clear:
> - barrier();
> - WRITE_ONCE(rb->aux_in_sampling, 0);
> -
> ring_buffer_put(rb);

I can't tell without applying these, if the labels still make sense. But
this one probably becomes "out_put" at this point.

Thanks,
--
Alex

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