linux-kernel - Re: [PATCH v6 1/3] perf/core: use rb trees for pinned/flexible groups

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Date:   Fri, 4 Aug 2017 16:53:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        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 v6 1/3] perf/core: use rb trees for pinned/flexible groups

On Thu, Aug 03, 2017 at 11:30:09PM +0300, Alexey Budankov wrote:
> On 03.08.2017 16:00, Peter Zijlstra wrote:
> > On Wed, Aug 02, 2017 at 11:13:54AM +0300, Alexey Budankov wrote:

> >> @@ -2759,13 +2932,13 @@ static void ctx_sched_out(struct perf_event_context *ctx,
> >>  
> >>  	perf_pmu_disable(ctx->pmu);
> >>  	if (is_active & EVENT_PINNED) {
> >> -		list_for_each_entry(event, &ctx->pinned_groups, group_entry)
> >> -			group_sched_out(event, cpuctx, ctx);
> >> +		perf_event_groups_iterate(&ctx->pinned_groups,
> >> +				group_sched_out_callback, &params);
> > 
> > So here I would expect to not iterate events where event->cpu !=
> > smp_processor_id() (and ideally not where event->pmu != ctx->pmu).
> >
> 
> We still need to iterate thru all groups on thread context switch in 
> and out as well as iterate thru cpu == -1 list (software events) additionally 
> to smp_processor_id() list from multiplexing timer interrupt handler.

Well, just doing the @cpu=-1 and @cpu=this_cpu subtrees is less work
than iterating _everything_, right?

The rest will not survive event_filter_match() anyway, so iterating them
is complete waste of time, and once we have them in a tree, its actually
easy to find this subset.