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

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Message-ID: <20170807083913.vfqmwsdzxsczh4yr@hirez.programming.kicks-ass.net>
Date:   Mon, 7 Aug 2017 10:39:13 +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 Mon, Aug 07, 2017 at 10:17:46AM +0300, Alexey Budankov wrote:
> Makes sense. The implementation becomes a bit simpler. The drawbacks 
> may be several rotations of potentially big tree on the critical path, 
> instead of updating four pointers in case of the tree of lists.

Yes, but like said, it allows implementing a better scheduler than RR,
allowing us to fix rotation artifacts where task runtimes are near the
rotation window.

A slightly more complicated, but also interested scheduling problem is
the per-cpu flexible vs the per-task flexible. Ideally we'd rotate them
at the same priority based on service, without strictly prioritizing the
per-cpu events.

Again, that is something that should be possible once we have a more
capable event scheduler.

So yes, cons and pros.. :-)