Re: [PATCH 1/7] perf: allow for PMU-specific event filtering

[Will Deacon]

Hi Mark,

On Wed, May 13, 2015 at 05:12:23PM +0100, Mark Rutland wrote:
> In certain circumstances it may not be possible to schedule particular
> events due to constraints other than a lack of hardware counters (e.g.
> on big.LITTLE systems where CPUs support different events). The core
> perf event code does not distinguish these cases and pessimistically
> assumes that any failure to schedule an event means that it is not worth
> attempting to schedule later events, even if some hardware counters are
> still unused.
> 
> When an event a pmu cannot schedule exists in a flexible group list it
> can unnecessarily prevent event groups following it in the list from
> being scheduled (until it is rotated to the end of the list). This means
> some events are scheduled for only a portion of the time they could be,
> and for short running programs no events may be scheduled if the list is
> initially sorted in an unfortunate order.
> 
> This patch adds a new (optional) filter_match function pointer to struct
> pmu which a pmu driver can use to tell perf core when an event matches
> pmu-specific scheduling requirements. This plugs into the existing
> event_filter_match logic, and makes it possible to avoid the scheduling
> problem described above. When no filter is provided by the PMU, the
> existing behaviour is retained.
> 
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Acked-by: Will Deacon <will.deacon@xxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> ---
>  include/linux/perf_event.h | 5 +++++
>  kernel/events/core.c       | 8 +++++++-
>  2 files changed, 12 insertions(+), 1 deletion(-)

Whilst I'm really keen to merge the architecture-specific parts of this
series, I'm going to need an Ack from one of the perf core maintainers
on this patch.

Peter, can you take a look please? (and I assume this is self-contained
enough not to conflict heavily with the current perf queue?).

Cheers,

Will

> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 61992cf..67c719c 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -304,6 +304,11 @@ struct pmu {
>  	 * Free pmu-private AUX data structures
>  	 */
>  	void (*free_aux)		(void *aux); /* optional */
> +
> +	/*
> +	 * Filter events for PMU-specific reasons.
> +	 */
> +	int (*filter_match)		(struct perf_event *event); /* optional */
>  };
>  
>  /**
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 81aa3a4..aaeb449 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1506,11 +1506,17 @@ static int __init perf_workqueue_init(void)
>  
>  core_initcall(perf_workqueue_init);
>  
> +static inline int pmu_filter_match(struct perf_event *event)
> +{
> +	struct pmu *pmu = event->pmu;
> +	return pmu->filter_match ? pmu->filter_match(event) : 1;
> +}
> +
>  static inline int
>  event_filter_match(struct perf_event *event)
>  {
>  	return (event->cpu == -1 || event->cpu == smp_processor_id())
> -	    && perf_cgroup_match(event);
> +	    && perf_cgroup_match(event) && pmu_filter_match(event);
>  }
>  
>  static void
> -- 
> 1.9.1
> 
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