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

From: Yunlong Song
Date: Sat Apr 25 2015 - 10:05:55 EST

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 -S

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

Yunlong Song

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