linux-kernel - Re: [PATCH v2 1/1] perf: Sharing PMU counters across compatible events

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Message-ID: <20180830151355.GA23723@krava>
Date:   Thu, 30 Aug 2018 17:13:55 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, lkp@...el.com, kernel-team@...com,
        Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>
Subject: Re: [PATCH v2 1/1] perf: Sharing PMU counters across compatible
 events

On Wed, Aug 15, 2018 at 10:03:13AM -0700, Song Liu wrote:

SNIP

>  
> +	perf_event_remove_dup(event, ctx);
>  	/*
>  	 * We can have double detach due to exit/hot-unplug + close.
>  	 */
> @@ -1982,6 +2123,92 @@ event_filter_match(struct perf_event *event)
>  	       perf_cgroup_match(event) && pmu_filter_match(event);
>  }
>  
> +/* PMU sharing aware version of event->pmu->add() */
> +static int event_pmu_add(struct perf_event *event,
> +			 struct perf_event_context *ctx)
> +{
> +	struct perf_event_dup *dup;
> +	int ret;
> +
> +	/* no sharing, just do event->pmu->add() */
> +	if (event->dup_id == -1)
> +		return event->pmu->add(event, PERF_EF_START);
> +
> +	dup = &ctx->dup_events[event->dup_id];
> +
> +	if (dup->active_event_count) {
> +		/* already enabled */
> +		dup->active_event_count++;
> +		dup->master->pmu->read(dup->master);
> +		event->dup_base_count = dup_read_count(dup);
> +		event->dup_base_child_count = dup_read_child_count(dup);
> +		return 0;
> +	}
> +
> +	/* try add master */
> +	ret = event->pmu->add(dup->master, PERF_EF_START);
> +
> +	if (!ret) {
> +		dup->active_event_count = 1;
> +		event->pmu->read(dup->master);
> +		event->dup_base_count = dup_read_count(dup);
> +		event->dup_base_child_count = dup_read_child_count(dup);

should you read the base before calling pmu->add ?
should be same for any dup event not just master

jirka