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:	Sat, 25 Apr 2015 22:05:36 +0800
From:	Yunlong Song <yunlong.song@...wei.com>
To:	David Ahern <dsahern@...il.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 2015/4/24 21:58, David Ahern wrote:
> 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
> 
> 
> 
> 

But this only shows the system call like strace, but we want the call stack of kernel functions
in fact.

-- 
Thanks,
Yunlong Song

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