Re: [RFC/PATCH] perf stat: Show sample events stat for a data file

From: Namhyung Kim
Date: Sat May 09 2015 - 10:40:39 EST

Hi Peter,

On Fri, May 08, 2015 at 04:46:20PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 29, 2015 at 08:58:22PM +0900, Namhyung Kim wrote:
> > > It would be nice if this thing could support 'perf record -s' which
> > > enables perf_event_attr::inherit_stat, which in turn results in
> > > PERF_RECORD_READ entries after every PERF_RECORD_EXIT which give the
> > > total number of events for each recorded task.
> >
> > Hmm.. this is one of the areas that I don't understand what's going
> > on. It'd be nice if you can help me understand and possibly improve
> > the doc too.
> >
> > So the combination of 'perf record -s' and 'perf report -T' should
> > show some per-thread counter values, right? I've found a bug on it.
> Right, they should. perf-record -s should give the event count per
> monitored thread, which when summed, should match what perf-stat gives
> for that workload.

Hmm.. I still don't understand what's the difference of those values
and the output of 'perf report -s pid --show-total-period'.

> And agreed on the bug, I can see it too.

I even think that 'perf report -T' should enforce to use --stdio (as
it's the only supported mode) and show a warning if used with --sort
or --parent option. I'll send a patch soon.

> > Anyway, I don't understand the numbers it shows.
> Me neither. I don't quite know why it has 5 cycles columns, we only
> measure the one cycles event.


> >
> > So the cycles values on 'perf report -T' are a lot more than the value
> > of perf stat. And I have no idea why it shows 5 different cycles for
> > each thread. Could you shed some light on this?
> Sadly no, not making sense. But I can confirm this is what it does.
> Lemme go poke at this, its weird.

OK, so I'll focus on the original event stat feature first, and then
look into the thread stat after you figure out something.

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