linux-kernel - Re: perf_counters issue with enable_on

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Date:	Tue, 25 Aug 2009 08:27:56 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	eranian@...il.com, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>,
	Andi Kleen <andi@...stfloor.org>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <cel@...ibm.com>,
	Corey J Ashford <cjashfor@...ibm.com>,
	Philip Mucci <mucci@...s.utk.edu>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	perfmon2-devel <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: perf_counters issue with enable_on_exec

Peter Zijlstra writes:

> 2. enable_on_exec only works on leaders, Paul, was that intended?

I think I thought that would be sufficient, but I guess it would be
cleaner if it also worked on non-leaders.

> 3. the scale stuff seems broken
> 
> # perf stat -e cycles -e instructions --repeat 10 true
> 
>  Performance counter stats for 'true' (10 runs):
> 
>         2612124  cycles                     ( +-   1.327% )
>         1870479  instructions             #      0.716 IPC     ( +-   0.132% )
> 
>     0.003743155  seconds time elapsed   ( +-   1.203% )
> 
> # ./test-enable_on_exec true
>              2651600 PERF_COUNT_HW_CPU_CYCLES 1111509 1111509 2651600.000000
>              1832720 PERF_COUNT_HW_INSTRUCTIONS 839395242 1111509 1384043177.264637
> 
> Paul, would a counter's time start running when its 'enabled' but part
> of a non-runnable group?

No, it shouldn't.  If it does it's a bug.

Paul.
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