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

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Date:   Mon, 7 Aug 2017 18:22:59 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 04.08.2017 17:53, Peter Zijlstra wrote:
> 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?

Right. That is actually the aim of this whole patch set - to avoid iterating "_everything_".

> 
> 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.
>