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

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Date:	Tue, 30 Oct 2012 16:42:44 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Dhaval Giani <dhaval.giani@...il.com>
Cc:	Arnaldo de Melo <acme@...radead.org>, mingo@...nel.org,
	Peter Zijlstra <peterz@...radead.org>,
	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

Hi Dhaval,

On Mon, 29 Oct 2012 12:45:53 -0400, Dhaval Giani wrote:
> 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

You meant $WAITPID, right?


>> kill $KILLPID

Doesn't it kill the last load generator only?


>> 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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