linux-kernel - Re: [PATCH 01/35] perf tools: Fix dso

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Date:   Tue, 19 Jul 2022 16:16:33 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 01/35] perf tools: Fix dso_id inode generation comparison

Em Tue, Jul 19, 2022 at 08:13:18AM -0700, Ian Rogers escreveu:
> On Tue, Jul 19, 2022 at 3:18 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
> >
> > On 18/07/22 17:57, Arnaldo Carvalho de Melo wrote:
> > > Em Mon, Jul 11, 2022 at 12:31:44PM +0300, Adrian Hunter escreveu:
> > >> Synthesized MMAP events have zero ino_generation, so do not compare zero
> > >> values.
> > >>
> > >> Fixes: 0e3149f86b99 ("perf dso: Move dso_id from 'struct map' to 'struct dso'")
> > >> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> > >> ---
> > >>  tools/perf/util/dsos.c | 10 ++++++++--
> > >>  1 file changed, 8 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
> > >> index b97366f77bbf..839a1f384733 100644
> > >> --- a/tools/perf/util/dsos.c
> > >> +++ b/tools/perf/util/dsos.c
> > >> @@ -23,8 +23,14 @@ static int __dso_id__cmp(struct dso_id *a, struct dso_id *b)
> > >>      if (a->ino > b->ino) return -1;
> > >>      if (a->ino < b->ino) return 1;
> > >>
> > >> -    if (a->ino_generation > b->ino_generation) return -1;
> > >> -    if (a->ino_generation < b->ino_generation) return 1;
> > >> +    /*
> > >> +     * Synthesized MMAP events have zero ino_generation, so do not compare
> > >> +     * zero values.
> > >> +     */
> > >> +    if (a->ino_generation && b->ino_generation) {
> > >> +            if (a->ino_generation > b->ino_generation) return -1;
> > >> +            if (a->ino_generation < b->ino_generation) return 1;
> > >> +    }
> > >
> > > But comparing didn't harm right? when its !0 now we may have three
> > > comparisions instead of 2 :-\
> > >
> > > The comment has some value tho, so I'm merging this :-)
> >
> > Thanks. I found it harmful because the mismatch resulted in a new
> > dso that did not have a build ID whereas the original dso did have
> > a build ID.  The build ID was essential because the object was not
> > found otherwise.
> 
> That's good to know, could we add that also to the comment? Perhaps:
> 
> Synthesized MMAP events have zero ino_generation, avoid comparing them
> with MMAP events with actual ino_generation.

I see now, thanks, adding this comment.

- Arnaldo