linux-kernel - Re: [PATCH 07/11] perf, tools: Collapse identically named events in perf stat

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Date:   Wed, 18 Jan 2017 08:31:26 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andi Kleen <andi@...stfloor.org>, acme@...nel.org,
        jolsa@...nel.org, linux-kernel@...r.kernel.org, mingo@...nel.org
Subject: Re: [PATCH 07/11] perf, tools: Collapse identically named events in
 perf stat

> > % perf stat  -a  -e unc_c_llc_lookup.any sleep 1
> > 
> >  Performance counter stats for 'system wide':
> > 
> >          2,685,120 Bytes unc_c_llc_lookup.any
> > 
> >        1.002648032 seconds time elapsed
> 
> 
> if one of them is not supported, we get wrong output:

I would argue the output is not incorrect, after all it is not supported
if something is missing. 

Imagine this is run with an interval:

If we changed the number of output lines based on some dynamic scheduling
condition this could confuse post processing scripts or users. Some output
records would be completely different than others. So marking everything
merged <not supported> in these cases is better and more consistent.

It is also difficult to change and should be a rare condition.

-Andi