linux-kernel - Re: [PATCH v3 3/9] perf annotate: Fix wrong --show-total-period option showing number of samples

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Date:   Sun, 23 Jul 2017 08:46:20 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Taeung Song <treeze.taeung@...il.com>,
        linux-kernel@...r.kernel.org, Milian Wolff <milian.wolff@...b.com>,
        Jiri Olsa <jolsa@...hat.com>, kernel-team@....com,
        Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v3 3/9] perf annotate: Fix wrong --show-total-period
 option showing number of samples

On Sun, Jul 23, 2017 at 07:46:05AM +0900, Namhyung Kim wrote:
> Hi Arnaldo and Taeung,
> 
> (+ Andi)
> 
> On Fri, Jul 21, 2017 at 11:47:48AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Jul 20, 2017 at 06:36:55AM +0900, Taeung Song escreveu:
> > > +++ b/tools/perf/builtin-annotate.c
> > > @@ -177,14 +177,12 @@ static int perf_evsel__add_sample(struct perf_evsel *evsel,
> > >  	 */
> > >  	process_branch_stack(sample->branch_stack, al, sample);
> > >  
> > > -	sample->period = 1;
> > >  	sample->weight = 1;
> > > -
> > >  	he = hists__add_entry(hists, al, NULL, NULL, NULL, sample, true);
> > >  	if (he == NULL)
> > >  		return -ENOMEM;
> > 
> > I split the hunk above into a separate patch, as a fix, Namhyung, can
> > you take a look at why need to unconditionally overwrite what is in
> > sample->weight as well?
> > 
> > Looks fishy as it may come with a value from the kernel, parsed in
> > perf_evsel__parse_sample(), when PERF_SAMPLE_WEIGHT is in
> > perf_event_attr->sample_type.
> > 
> > Is it that the hists code needs a sane value when PERF_SAMPLE_WEIGHT
> > isn't requested in sample_type?
> 
> It was Andi added that code originally (05484298cbfe).  IIUC the
> weight is only meaningful for some CPUs with Intel TSX and he used a
> dummy value.

It's used for more than TSX. e.g. perf mem uses it for memory latencies.

> AFAIK the hists code doesn't care of it unless weight sort key is used
> (for report).  As it's not used by annotate code, I think it'd be
> better leaving it as is (like period).

Right, it's needed when weight is specified as a sort key. But we need
a fallback in case the user specified weight in perf report, but
didn't enable it for perf record.

-Andi