linux-kernel - Re: [BUG] perf report: different reports when run on terminal as opposed to script

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Date:	Mon, 29 Oct 2012 12:45:53 -0400
From:	Dhaval Giani <dhaval.giani@...il.com>
To:	Arnaldo de Melo <acme@...radead.org>, mingo@...nel.org,
	Peter Zijlstra <peterz@...radead.org>, namhyung@...nel.org
Cc:	akshay kumar <iit.akshay@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] perf report: different reports when run on terminal as
 opposed to script

On Mon, Oct 29, 2012 at 12:01 PM, Dhaval Giani <dhaval.giani@...il.com> wrote:
> Hi,
>
> As part of a class assignment I have to collect some performance
> statistics. In order to do so I run
>
> perf record -g <the program I have to profile>
>
> And in another window, I start 200 threads of the load generator
> (which is not recorded by perf)
>
> This generates me statistics that I expect to see, and I am happy. As
> this is academia and a class assignment, I need to collect information
> and analyze it across different setups. Which of course meant I script
> this whole thing, which basically is
>
> for i in all possibilities
> do
> perf record -g <the program I have to profile> &
> WAITPID=$!
> for j in NR_THREADS
> do
> <start load generator> &
> KILLPID=$!
> done
> wait $PID
> kill $KILLPID
> mv perf.data results/perf.data.$i
> done
>
> (This is basic pseudo script of what I am doing), which results me
> having my profile being topped by _vscanf() and the function which I
> was seeing dominating in the older report dropping down to something
> like 5% (as opposed to 16-17%)
>
> Have I misunderstood how perf works? Something deeper? I am currently
> on 3.6.3. I can update to the latest upstream and report back. Any
> debug code is very welcome. I can also make my toy program and the
> scripts available for you to try out.

I just updated to 6b0cb4eef7bdaa27b8021ea81813fba330a2d94d and I still
see this happen.

Thanks!
Dhaval
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