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

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Date:   Wed, 18 Jan 2017 17:56:31 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andi Kleen <ak@...ux.intel.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

On Wed, Jan 18, 2017 at 08:31:26AM -0800, Andi Kleen wrote:
> > > % 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.

will it always show 'not supported', as I haven't found this in the
changelog I guess you did not know about this behaviour?

could you also please document it somewhere

jirka