linux-kernel - Re: [RFC][PATCH] perf: Rewrite core context handling

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Message-ID: <9DFB7D45-76CD-4E77-8360-FBCE1AD9A78F@fb.com>
Date:   Tue, 23 Oct 2018 06:13:29 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Ingo Molnar <mingo@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "alexey.budankov@...ux.intel.com" <alexey.budankov@...ux.intel.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "megha.dey@...el.com" <megha.dey@...el.com>,
        "frederic@...nel.org" <frederic@...nel.org>
Subject: Re: [RFC][PATCH] perf: Rewrite core context handling

Hi Peter,

> On Oct 10, 2018, at 3:45 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> Hi all,
> 
> There have been various issues and limitations with the way perf uses
> (task) contexts to track events. Most notable is the single hardware PMU
> task context, which has resulted in a number of yucky things (both
> proposed and merged).
> 
> Notably:
> 
> - HW breakpoint PMU
> - ARM big.little PMU
> - Intel Branch Monitoring PMU
> 
> Since we now track the events in RB trees, we can 'simply' add a pmu
> order to them and have them grouped that way, reducing to a single
> context. Of course, reality never quite works out that simple, and below
> ends up adding an intermediate data structure to bridge the context ->
> pmu mapping.
> 
> Something a little like:
> 
>              ,------------------------[1:n]---------------------.
>              V                                                  V
>    perf_event_context <-[1:n]-> perf_event_pmu_context <--- perf_event
>              ^                      ^     |                     |
>              `--------[1:n]---------'     `-[n:1]-> pmu <-[1:n]-'
> 
> This patch builds (provided you disable CGROUP_PERF), boots and survives
> perf-top without the machine catching fire.
> 
> There's still a fair bit of loose ends (look for XXX), but I think this
> is the direction we should be going.
> 
> Comments?

This might be a little off topic...

What's you plan about this effort and the PMU sharing work 
(https://lkml.org/lkml/2018/10/4/10)? Would PMU sharing work better/simpler
with this effort? 

Thanks,
Song