linux-kernel - Re: [PATCH v7 1/2] perf/core: use rb trees for pinned/flexible groups

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Date:   Wed, 23 Aug 2017 14:17:29 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>, Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Stephane Eranian <eranian@...gle.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/2] perf/core: use rb trees for pinned/flexible groups

Alexey Budankov <alexey.budankov@...ux.intel.com> writes:

> @@ -3091,61 +3231,55 @@ static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx,
>  }
>  
>  static void
> -ctx_pinned_sched_in(struct perf_event_context *ctx,
> -		    struct perf_cpu_context *cpuctx)
> +ctx_pinned_sched_in(struct perf_event *event,
> +		   struct perf_cpu_context *cpuctx,
> +		   struct perf_event_context *ctx)

If you're doing this, you also need to rename the function, because it
now schedules in one event and not a context. But better just keep it as
is.

>  {
> -	struct perf_event *event;
> -
> -	list_for_each_entry(event, &ctx->pinned_groups, group_entry) {

Why not put your new iterator here in place of the old one, instead of
moving things around? Because what follows is hard to read and is also
completely unnecessary:

> -		if (event->state <= PERF_EVENT_STATE_OFF)
> -			continue;
> -		if (!event_filter_match(event))
> -			continue;
> +	if (event->state <= PERF_EVENT_STATE_OFF)
> +		return;
> +	if (!event_filter_match(event))
> +		return;

like this,

>  
> -		/* may need to reset tstamp_enabled */
> -		if (is_cgroup_event(event))
> -			perf_cgroup_mark_enabled(event, ctx);
> +	/* may need to reset tstamp_enabled */
> +	if (is_cgroup_event(event))
> +		perf_cgroup_mark_enabled(event, ctx);

or this

>  
> -		if (group_can_go_on(event, cpuctx, 1))
> -			group_sched_in(event, cpuctx, ctx);
> +	if (group_can_go_on(event, cpuctx, 1))
> +		group_sched_in(event, cpuctx, ctx);

etc, etc.

> @@ -3156,7 +3290,8 @@ ctx_sched_in(struct perf_event_context *ctx,
>  	     struct task_struct *task)
>  {
>  	int is_active = ctx->is_active;
> -	u64 now;

Why?

> +	struct perf_event *event;
> +	struct rb_node *node;
>  
>  	lockdep_assert_held(&ctx->lock);
>  
> @@ -3175,7 +3310,7 @@ ctx_sched_in(struct perf_event_context *ctx,
>  
>  	if (is_active & EVENT_TIME) {
>  		/* start ctx time */
> -		now = perf_clock();
> +		u64 now = perf_clock();

Why?

>  		ctx->timestamp = now;
>  		perf_cgroup_set_timestamp(task, ctx);
>  	}
> @@ -3185,11 +3320,19 @@ ctx_sched_in(struct perf_event_context *ctx,
>  	 * in order to give them the best chance of going on.
>  	 */
>  	if (is_active & EVENT_PINNED)
> -		ctx_pinned_sched_in(ctx, cpuctx);
> +		perf_event_groups_for_each(event, node,
> +				&ctx->pinned_groups, group_node,
> +				group_list, group_entry)
> +			ctx_pinned_sched_in(event, cpuctx, ctx);

So this perf_event_groups_for_each() can just move into
ctx_*_sched_in(), can't it?

Regards,
--
Alex