linux-kernel - Re: [PATCH 2/2] perf tool: don't print bogus data on -e cycles

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Date:	Tue, 1 Oct 2013 10:48:53 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Ramkumar Ramachandra <artagnon@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 2/2] perf tool: don't print bogus data on -e cycles


* Ramkumar Ramachandra <artagnon@...il.com> wrote:

> When only the cycles event is requested:
> 
> $ perf stat -e cycles dd if=/dev/zero of=/dev/null count=1000000
> 1000000+0 records in
> 1000000+0 records out
> 512000000 bytes (512 MB) copied, 0.26123 s, 2.0 GB/s
> 
>  Performance counter stats for 'dd if=/dev/zero of=/dev/null count=1000000':
> 
>        911,626,453 cycles                    #    0.000 GHz
> 
>        0.262113350 seconds time elapsed
> 
> The 0.000 GHz comment in the output is totally bogus and misleading. It
> happens because update_shadow_stats() doesn't touch runtime_nsecs_stats;
> it is only written when a requested counter matches a SW_TASK_CLOCK. In
> our case, since we have only requested HW_CPU_CYCLES,
> runtime_nsecs_stats is unavailable. So, omit printing the comment
> altogether.
> 
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
> Signed-off-by: Ramkumar Ramachandra <artagnon@...il.com>
> ---
>  tools/perf/builtin-stat.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo
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