linux-kernel - Re: [PATCH v6 04/10] libperf: Add evsel mmap support

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Message-ID: <CAL_Jsq+c2suLcGUuXZ-a4UG-Bte-+uVfYjB-+BYXDbAYEf2Jyg@mail.gmail.com>
Date:   Wed, 31 Mar 2021 17:06:46 -0500
From:   Rob Herring <robh@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ian Rogers <irogers@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Honnappa Nagarahalli <honnappa.nagarahalli@....com>,
        Zachary.Leaf@....com, Raphael Gault <raphael.gault@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 04/10] libperf: Add evsel mmap support

On Fri, Mar 12, 2021 at 12:29 PM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Fri, Mar 12, 2021 at 07:34:39AM -0700, Rob Herring wrote:
> > On Fri, Mar 12, 2021 at 6:59 AM Jiri Olsa <jolsa@...hat.com> wrote:
> > >
> > > On Wed, Mar 10, 2021 at 05:08:31PM -0700, Rob Herring wrote:
> > >
> > > SNIP
> > >
> > > > +
> > > >  static int
> > > >  sys_perf_event_open(struct perf_event_attr *attr,
> > > >                   pid_t pid, int cpu, int group_fd,
> > > > @@ -137,6 +147,8 @@ void perf_evsel__free_fd(struct perf_evsel *evsel)
> > > >  {
> > > >       xyarray__delete(evsel->fd);
> > > >       evsel->fd = NULL;
> > > > +     xyarray__delete(evsel->mmap);
> > > > +     evsel->mmap = NULL;
> > > >  }
> > > >
> > > >  void perf_evsel__close(struct perf_evsel *evsel)
> > > > @@ -156,6 +168,45 @@ void perf_evsel__close_cpu(struct perf_evsel *evsel, int cpu)
> > > >       perf_evsel__close_fd_cpu(evsel, cpu);
> > > >  }
> > > >
> > > > +int perf_evsel__mmap(struct perf_evsel *evsel, int pages)
> > > > +{
> > > > +     int ret, cpu, thread;
> > > > +     struct perf_mmap_param mp = {
> > > > +             .prot = PROT_READ | PROT_WRITE,
> > > > +             .mask = (pages * page_size) - 1,
> > > > +     };
> > >
> > > I don't mind using evsel->fd for dimensions below,
> > > but we need to check in here that it's defined,
> > > that perf_evsel__open was called
> >
> > Right, so I'll add this here:
> >
> > if (evsel->fd == NULL)
> >     return -EINVAL;

Actually, pretty much none of the API checks this.
perf_evsel__run_ioctl(), perf_evsel__enable(), perf_evsel__disable(),
perf_evsel__read() will all just deference evsel->fd. So fix all of
these or follow existing behavior?


> > Note that struct evsel has dimensions in it, but they are only set in
> > the evlist code. I couldn't tell if that was by design or mistake.
>
> we do? we have the cpus and threads in perf_evsel no?

Right, perf_evsel has cpus and threads pointers which in turn have the
sizes, but those pointers are not set within the evsel code.

> also you'd need perf_evsel not evsel, right?
>
> >
> > BTW, I just noticed perf_evsel__open is leaking memory on most of its
> > error paths.
>
> nice.. let's fix it ;-)

NM, I missed that they are static...

Rob