linux-kernel - Re: [PATCH] perf test x86: address multiplexing in rdpmc test

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Message-ID: <20200322083544.GE2452@worktop.programming.kicks-ass.net>
Date:   Sun, 22 Mar 2020 09:35:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf test x86: address multiplexing in rdpmc test

On Sat, Mar 21, 2020 at 10:44:49AM -0700, Ian Rogers wrote:
> On Sat, Mar 21, 2020 at 6:41 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Fri, Mar 20, 2020 at 05:14:00PM -0700, Ian Rogers wrote:
> > > Counters may be being used for pinned or other events which inhibit the
> > > instruction counter in the test from being scheduled - time_enabled > 0
> > > but time_running == 0. This causes the test to fail with division by 0.
> > > Add a sleep loop to ensure that the counter is run before computing
> > > the count.

> > > +
> > > +                     if (running == 0) {
> >
> > This is not in fact the condition the Changelog calls out.
> 
> Not sure I follow. As in the multiplexing? It is exactly the condition
> that time_running == 0.

I meant the condition should be 'enabled && !running'.