linux-kernel - Re: [PATCH] perf c2c: Fix sorting.

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Date:   Tue, 14 Jan 2020 13:28:55 -0300
From:   Arnaldo Carvalho de Melo <acme@...hat.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andres Freund <andres@...razel.de>, linux-kernel@...r.kernel.org,
        Jiri Olsa <jolsa@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org
Subject: Re: [PATCH] perf c2c: Fix sorting.

Em Thu, Jan 09, 2020 at 10:46:11PM +0100, Jiri Olsa escreveu:
> On Thu, Jan 09, 2020 at 09:00:41AM -0800, Andres Freund wrote:
> 
> SNIP
> 
> > > >  tools/perf/builtin-c2c.c | 10 ++++++----
> > > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/tools/perf/builtin-c2c.c b/tools/perf/builtin-c2c.c
> > > > index e69f44941aad..f2e9d2b1b913 100644
> > > > --- a/tools/perf/builtin-c2c.c
> > > > +++ b/tools/perf/builtin-c2c.c
> > > > @@ -595,8 +595,8 @@ tot_hitm_cmp(struct perf_hpp_fmt *fmt __maybe_unused,
> > > >  {
> > > >  	struct c2c_hist_entry *c2c_left;
> > > >  	struct c2c_hist_entry *c2c_right;
> > > > -	unsigned int tot_hitm_left;
> > > > -	unsigned int tot_hitm_right;
> > > > +	uint64_t tot_hitm_left;
> > > > +	uint64_t tot_hitm_right;
> > > 
> > > that change looks right, but I can't see how that could
> > > happened because of change in Fixes: tag
> > > 
> > > was the return statement of this function:
> > > 
> > >         return tot_hitm_left - tot_hitm_right;
> > > 
> > > considered to be 'unsigned int' and then converted to int64_t,
> > > which would treat negative 'unsigned int' as big positive 'int64_t'?
> > 
> > Correct. So e.g. when comparing 1 and 2 tot_hitm, we'd get (int64_t)
> > UINT_MAX as a result, which is obviously wrong. However, due to
> > hist_entry__sort() returning int at the time, this was masked, as the
> > int64_t was cast to int. Thereby again yielding a negative number for
> > the comparisons of hist_entry__sort()'s result.  After
> > hist_entry__sort() was fixed however, there never could be negative
> > return values (but 0's are possible) of hist_entry__sort() for c2c.
> 
> I see.. ok
> 
> Acked-by: Jiri Olsa <jolsa@...hat.com>

Thanks, applied.

- Arnaldo