linux-kernel - Re: [PATCH 1/1] Fix number of events displayed in header

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Message-ID: <1332273597.18960.454.camel@twins>
Date:	Tue, 20 Mar 2012 20:59:57 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ashay Rane <ashay.r@...il.com>
Cc:	David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-perf-users@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Ashay Rane <ashay.rane@...c.utexas.edu>
Subject: Re: [PATCH 1/1] Fix number of events displayed in header

On Tue, 2012-03-20 at 14:51 -0500, Ashay Rane wrote:
> The problem I am seeing is that the `perf record' output does not
> comform with the output of `perf stat'. For example, for `hackbench 10
> process 1000', I see 19 x 10^9 cycles reported by `perf stat'.
> However, `perf report -n' prints "Events: 2K cycles" and `perf report
> -n --dso hackbench' prints "Events: 47 cycles". 

Ah, read it as if perf report is saying: Samples: 47 of event: cycles.

That is, its telling you the cycles event had 47 overflows causing 47
samples to be taken (IP, etc..) and written out.

The point of reporting this number is that it puts the accuracy of the
percentages into perspective. The more samples, the greater the coverage
and more accurate the actual percentage of time spend in the various
functions.
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