From: Andi Kleen <andi@firstfloor.org>
To: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: "linux-perf-use." <linux-perf-users@vger.kernel.org>
Subject: Re: Bogus PMCs on Linux 3.13
Date: Sat, 12 Mar 2016 06:12:46 -0800 [thread overview]
Message-ID: <87lh5nbx9d.fsf@tassilo.jf.intel.com> (raw)
In-Reply-To: <CAE40pdezFG8caviy4NMNjKkucoU2tp2cbjAPY-V66RJfUwe66g@mail.gmail.com> (Brendan Gregg's message of "Wed, 9 Mar 2016 12:48:06 -0800")
Brendan Gregg <brendan.d.gregg@gmail.com> writes:
>
> Performance counter stats for 'dd if=/dev/zero of=/dev/null bs=1024k
> count=10k':
>
> 1,784,251,390 cycles [33.80%]
> 388,784,218,053 instructions # 217.90 insns per
> cycle [34.25%]
The obvious problem is that you're multiplexing. Multiplexing can cause
large measuring errors. Try to stop whoever else uses perf.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
prev parent reply other threads:[~2016-03-12 14:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-09 20:48 Bogus PMCs on Linux 3.13 Brendan Gregg
2016-03-12 14:12 ` Andi Kleen [this message]
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