From: Andi Kleen <andi@firstfloor.org>
To: Harald Servat <harald.servat@bsc.es>
Cc: linux-perf-users@vger.kernel.org
Subject: Re: perf pebs sampling through stores + period is wrong?
Date: Thu, 20 Feb 2014 13:27:58 -0800 [thread overview]
Message-ID: <87eh2xcw4h.fsf@tassilo.jf.intel.com> (raw)
In-Reply-To: <5305E9AF.3050906@bsc.es> (Harald Servat's message of "Thu, 20 Feb 2014 12:40:31 +0100")
Harald Servat <harald.servat@bsc.es> writes:
>
> $ perf mem -t store record -c 10000 ./a.out
> ...
> [perf record: Woken up 4 times to write data]
> [perf record: Captured and wrote 0.921 MB perf.data (~40247 samples)]
>
> Notice that the number of samples raised by 20x, which to me seems
> very odd because the number of stores was half, so I expected 0.5x
> here. Or am I supposing this the wrong way?
Likely you're throttling. 10k is a far too low period for such
measurements
(The cpu can do multiple stores per cycle and it runs at multiple
Ghz. Each PMI takes many thousands of cycles. You can do the math.)
-Andi
--
ak@linux.intel.com -- Speaking for myself only
next prev parent reply other threads:[~2014-02-20 21:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-20 11:40 perf pebs sampling through stores + period is wrong? Harald Servat
2014-02-20 21:27 ` Andi Kleen [this message]
2014-02-21 9:45 ` Harald Servat
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