linux-kernel - Re: [RFC][PATCH] perf: Rewrite enabled/running timekeeping

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Date:   Mon, 4 Sep 2017 17:41:45 +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>,
        Vince Weaver <vince@...ter.net>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH] perf: Rewrite enabled/running timekeeping

On Mon, Sep 04, 2017 at 05:56:06PM +0300, Alexey Budankov wrote:
> On 04.09.2017 15:08, Peter Zijlstra wrote:
> > On Mon, Sep 04, 2017 at 01:46:45PM +0300, Alexey Budankov wrote:
> >>> So the below completely rewrites timekeeping (and probably breaks
> >>> world) but does away with the need to touch events that don't get
> >>> scheduled.
> >>
> >> We still need and do iterate thru all events at some points e.g. on context switches.
> > 
> > Why do we _need_ to?
> 
> We do so in the current implementation with several tstamp_* fields.

Right, but we want to stop doing so asap :-)


> >> U - allocation, A - ACTIVE, I - INACTIVE, O - OFF, 
> >> E - ERROR, X - EXIT, D - DEAD,
> > 
> > Not sure we care about the different <0 values, they're all effectively
> > OFF.
> 
> We still need to care about proper initial state of timings when moving above >=0 state.

Very true. I'm not sure I fully covered that, let me see if there's
something sensible to do for that.