linux-kernel - Re: [PATCH v1 2/2] perf test: Avoid infinite loop for task exit case

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Date:   Tue, 15 Oct 2019 11:20:38 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] perf test: Avoid infinite loop for task exit case

On Mon, Oct 14, 2019 at 11:11:36AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Oct 11, 2019 at 05:19:42PM +0800, Leo Yan escreveu:
> > When execute task exit testing case, Perf tool stucks in this case and
> > doesn't return back on Arm64 Juno board.
> > 
> > After dig into this issue, since Juno board has Arm's big.LITTLE CPUs,
> > thus the PMUs are not compatible between the big CPUs and little CPUs.
> > This leads to PMU event cannot be enabled properly when the traced task
> > is migrated from one variant's CPU to another variant.  Finally, the
> > test case runs into infinite loop for cannot read out any event data
> > after return from polling.
> > 
> > Eventually, we need to work out formal solution to allow PMU events can
> > be freely migrated from one CPU variant to another, but this is a
> > difficult task and a different topic.  This patch tries to fix the Perf
> > test case to avoid infinite loop, when the testing detects 1000 times
> > retrying for reading empty events, it will directly bail out and return
> > failure.  This allows the Perf tool can continue its other test cases.
> 
> Thanks, applied.

Thanks a lot, Arnaldo.