linux-kernel - Re: [Question] How does perf still record the stack of a specified pid even when that process is interrupted and CPU is scheduled to other process

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Date:	Fri, 24 Apr 2015 07:58:48 -0600
From:	David Ahern <dsahern@...il.com>
To:	Yunlong Song <yunlong.song@...wei.com>, a.p.zijlstra@...llo.nl,
	paulus@...ba.org, mingo@...hat.com,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	linux-kernel@...r.kernel.org, wangnan0@...wei.com
Subject: Re: [Question] How does perf still record the stack of a specified
 pid even when that process is interrupted and CPU is scheduled to other process

On 4/24/15 7:31 AM, Yunlong Song wrote:
> Now we are profiling the performance of ext4 and f2fs on an eMMC card with iozone,
> we find a case that ext4 is better than f2fs in random write under the test of
> "iozone -s 262144 -r 64 -i 0 -i 2". We want to analyze the I/O delay of the two
> file systems. We have got a conclusion that 1% of sys_write takes up 60% time of
> the overall sys_write (262144/64=4096). We want to find out the call stack during
> this specific 1% sys_write. Our idea is to record the stack in a certain time period
> and since the specific 1% case takes up 60% time, the total number of records of its
> stack should also takes up 60% of the total records, then we can recognize those stacks
> and figure out what the I/O stack of f2fs is doing in the 1% case.

And to address this specific profiling problem have you tried:

    perf trace record -- iozone ...
    perf trace -i perf.data -S


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