linux-kernel - Re: [PATCH v2 2/2] perf tools: ARM SPE code cleanup

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Message-ID: <CANLsYkyEYhVvG-z0+EXUSjgsQJ8EZtv7NbC1XRN_NGE8y5P2qQ@mail.gmail.com>
Date:   Tue, 28 Jul 2020 09:46:59 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Wei Li <liwei391@...wei.com>, Leo Yan <leo.yan@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kim Phillips <kim.phillips@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>
Subject: Re: [PATCH v2 2/2] perf tools: ARM SPE code cleanup

On Tue, 28 Jul 2020 at 06:02, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>
> Em Mon, Jul 27, 2020 at 02:34:36PM -0600, Mathieu Poirier escreveu:
> > On Fri, Jul 24, 2020 at 03:11:11PM +0800, Wei Li wrote:
> > > - Firstly, the function auxtrace_record__init() will be invoked only
> > >   once, the variable "arm_spe_pmus" will not be used afterwards, thus
> > >   we don't need to check "arm_spe_pmus" is NULL or not;
> > > - Another reason is, even though SPE is micro-architecture dependent,
> > >   but so far it only supports "statistical-profiling-extension-v1" and
> > >   we have no chance to use multiple SPE's PMU events in Perf command.
> >
> > I find the above changelog somewhat out of touch with the patch itself.  The
> > only thing that is happening here is the removal of a useless check and a fix
> > for a memory leak.
>
> Humm, I think the original intent of that code was to cache the results
> of find_all_arm_spe_pmus(), as the variable it is assigned to is static.

Correct, but as you pointed out below the function is called only
once.  And there is still a leak as that memory is never freed.

>
> So not a leak, as there was that static reference to it to reuse it
> later, but that is strange in a function named "__init()" which usually
> is called only once, anyway, so I think that the paragraph with
> "Firstly" is kinda ok, but confusing, I think it should read:
>
> - auxtrace_record__init() is called only once, so there is no point in
>   using a static variable to cache the results of
>   find_all_arm_spe_pmus(), make it local and free the results after use.

This is exactly what this patch does and what the changelog should read.

>
> The second paragraph is SPE specific, so I'm not qualified to judge on
> it.
>
> I'm replacing the first paragraph with the version I wrote and keep it
> in my local branch, please holler if you think I misunderstood.
>

There is no point for the next paragraph, it has no relevance to what
the code is doing.

Thanks for the editing.

> - Arnaldo
>
> > Once again whether Arnaldo wants to make the changes by hand or not you may have
> > to resubmit.
> >
> > Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> >
> > >
> > > So remove the useless check code to make it clear.
> > >
> > > Signed-off-by: Wei Li <liwei391@...wei.com>
> > > ---
> > >  tools/perf/arch/arm/util/auxtrace.c | 9 ++++-----
> > >  1 file changed, 4 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/tools/perf/arch/arm/util/auxtrace.c b/tools/perf/arch/arm/util/auxtrace.c
> > > index 28a5d0c18b1d..b187bddbd01a 100644
> > > --- a/tools/perf/arch/arm/util/auxtrace.c
> > > +++ b/tools/perf/arch/arm/util/auxtrace.c
> > > @@ -57,17 +57,15 @@ struct auxtrace_record
> > >     struct evsel *evsel;
> > >     bool found_etm = false;
> > >     struct perf_pmu *found_spe = NULL;
> > > -   static struct perf_pmu **arm_spe_pmus = NULL;
> > > -   static int nr_spes = 0;
> > > +   struct perf_pmu **arm_spe_pmus = NULL;
> > > +   int nr_spes = 0;
> > >     int i = 0;
> > >
> > >     if (!evlist)
> > >             return NULL;
> > >
> > >     cs_etm_pmu = perf_pmu__find(CORESIGHT_ETM_PMU_NAME);
> > > -
> > > -   if (!arm_spe_pmus)
> > > -           arm_spe_pmus = find_all_arm_spe_pmus(&nr_spes, err);
> > > +   arm_spe_pmus = find_all_arm_spe_pmus(&nr_spes, err);
> > >
> > >     evlist__for_each_entry(evlist, evsel) {
> > >             if (cs_etm_pmu &&
> > > @@ -84,6 +82,7 @@ struct auxtrace_record
> > >                     }
> > >             }
> > >     }
> > > +   free(arm_spe_pmus);
> > >
> > >     if (found_etm && found_spe) {
> > >             pr_err("Concurrent ARM Coresight ETM and SPE operation not currently supported\n");
> > > --
> > > 2.17.1
> > >
>
> --
>
> - Arnaldo