linux-kernel - RE: [PATCH] perf/core: introduce context per CPU event list

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Date:   Thu, 10 Nov 2016 14:31:04 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "vince@...ter.net" <vince@...ter.net>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "andi@...stfloor.org" <andi@...stfloor.org>
Subject: RE: [PATCH] perf/core: introduce context per CPU event list



> > I don't think those need be tracked at all, they're immaterial for
> > actual scheduling. Once we ioctl() them back to life we can insert
> > them into the tree.
> 
> Sure, that sounds fine for scheduling (including big.LITTLE).
> 
> I might still be misunderstanding something, but I don't think that helps
> Kan's case: since INACTIVE events which will fail their filters (including the
> CPU check) will still be in the tree, they will still have to be iterated over.
> 
> That is, unless we also sort the tree by event->cpu, or if in those cases we
> only care about ACTIVE events and can use an active list.

Yes, if we can sort the tree by event->cpu, we can minimize the iteration in
the perf_iterate_ctx. That should help on reducing the overhead.


Thanks,
Kan