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

[Namhyung Kim <namhyung@kernel.org>]

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.

Right.

> 
> > 
> > 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.

Thanks,
Namhyung