linux-kernel - RE: [RFC 3/6] perf/core: use rb-tree to sched in event groups

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Date:   Thu, 12 Jan 2017 13:28:48 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     David Carrillo-Cisneros <davidcc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>, Borislav Petkov <bp@...e.de>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Vince Weaver <vince@...ter.net>, Paul Turner <pjt@...gle.com>,
        "Stephane Eranian" <eranian@...gle.com>
Subject: RE: [RFC 3/6] perf/core: use rb-tree to sched in event groups



> On Wed, Jan 11, 2017 at 08:31:11PM +0000, Liang, Kan wrote:
> 
> > > Kan, in your per-cpu event list patch you mentioned that you saw a
> > > large overhead in perf_iterate_ctx() when skipping events for other
> CPUs.
> > > Which callers of perf_iterate_ctx() specifically was that
> > > problematic for? Do those callers only care about the *active* events,
> for example?
> >
> > Based on my test, the large overhead was observed in perf_iterate_sb.
> > Yes, it only cares about the *active* events.
>

Oh Sorry, my bad. My brain must not be working yesterday...
I just re-visited the code. The *inactive* also need to be checked.
	if (event->state < PERF_EVENT_STATE_INACTIVE)
		continue;
So the perf_iterate_sb iterates through all events (both STATE_ACTIVE
and STATE_INACTIVE).

I'm not sure if it is enough to only take care of *active* events.
Peter may comments on it.

Thanks,
Kan

> Great!
> 
> That should mean the first patch of this series (adding the active events
> lists) should give us sufficient infrastructure to solve that particular issue.
> 
> Thanks,
> Mark.