linux-kernel - Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

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Message-ID: <20200914193856.GN1714160@krava>
Date:   Mon, 14 Sep 2020 21:38:56 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <song@...nel.org>
Cc:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Song Liu <songliubraving@...com>,
        "Frank Ch. Eigler" <fche@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

On Sun, Sep 13, 2020 at 11:20:31PM -0700, Song Liu wrote:
> On Sun, Sep 13, 2020 at 10:40 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Mon, Sep 14, 2020 at 6:03 AM Jiri Olsa <jolsa@...nel.org> wrote:
> > >
> > > Add new version of mmap event. The MMAP3 record is an
> > > augmented version of MMAP2, it adds build id value to
> > > identify the exact binary object behind memory map:
> > >
> > >   struct {
> > >     struct perf_event_header header;
> > >
> > >     u32                      pid, tid;
> > >     u64                      addr;
> > >     u64                      len;
> > >     u64                      pgoff;
> > >     u32                      maj;
> > >     u32                      min;
> > >     u64                      ino;
> > >     u64                      ino_generation;
> > >     u32                      prot, flags;
> > >     u32                      reserved;
> 
> I guess we need reserved _after_ buildid, no?

it's there to align the size to 8 bytes,
so the sample_id is in proper place

but yes, perhaps after buildid would make more sense

> 
> > >     u8                       buildid[20];
> >
> > Do we need maj, min, ino, ino_generation for mmap3 event?
> > I think they are to compare binaries, then we can do it with
> > build-id (and I think it'd be better)..
> 
> +1 we shouldn't need maj, min, etc.

right, and as peter already wrote buildid could fit
in that space.. yay :)

thanks,
jirka

> 
> Thanks,
> Song
> 
> [...]
>