From: Andi Kleen <andi@firstfloor.org>
To: Manuel Selva <selva.manuel@gmail.com>
Cc: linux-perf-users@vger.kernel.org
Subject: Re: Understanding perf mem -t load results
Date: Tue, 07 Jan 2014 13:27:01 -0800 [thread overview]
Message-ID: <87wqib4h5m.fsf@tassilo.jf.intel.com> (raw)
In-Reply-To: <CALbiyZyUncZZq7mU=+Hk9mYY7q3ugWiiESWSS9RSP-PfwB9u=w@mail.gmail.com> (Manuel Selva's message of "Tue, 7 Jan 2014 16:06:18 +0100")
Manuel Selva <selva.manuel@gmail.com> writes:
> The perf mem record tool use the
> MEM_INST_RETIRED.LATENCY_ABOVE_THRESHOLD which I guess belongs to the
> memory PEBS events you mentionned (isn't it ?) is reporting
Yes.
> information about the sources of the events. it seems that for this
> purpose the IP information is used, does it mean that what perf mem
> reports can be wrong because of the random IP selection mechanism you
> mentionned ?
The CPU can theoretically execute billions of loads/stores every second.
There is no way any reporting mechanism can keep up with that.
So the only thing you can do is to sample (only collect
every N operations), with a fairly large period.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
next prev parent reply other threads:[~2014-01-07 21:27 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-12 14:06 Understanding perf mem -t load results Manuel Selva
2013-12-15 18:27 ` Manuel Selva
2013-12-15 21:18 ` Andi Kleen
2013-12-15 22:03 ` Manuel Selva
2013-12-15 23:45 ` Andi Kleen
2013-12-16 9:13 ` Manuel Selva
2013-12-20 9:38 ` Manuel Selva
2013-12-24 2:18 ` Andi Kleen
2013-12-24 7:10 ` Manuel Selva
2013-12-24 7:28 ` Andi Kleen
2013-12-24 7:42 ` Manuel Selva
2013-12-24 21:27 ` Andi Kleen
2013-12-25 10:25 ` Manuel Selva
2014-01-07 15:06 ` Manuel Selva
2014-01-07 21:27 ` Andi Kleen [this message]
2014-01-08 8:53 ` Manuel Selva
2014-01-08 9:50 ` Manuel Selva
2014-01-08 19:44 ` Andi Kleen
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