lkml.org 
[lkml]   [2015]   [May]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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 2015/4/25 23:53, David Ahern wrote:
> On 4/25/15 8:05 AM, Yunlong Song wrote:
>> 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.
>>
>
> We haven't added the callchain option yet; on the to-do list.
>
> perf trace record -g -- iozone ...
> perf trace -i perf.data -s
> --> summary of system calls, max/min/average times
>
> perf trace -i perf.data --duration 10.0 -T
> --> note the timestamp where the write took a "long" time
>
> perf script
> --> search down to *around* the time of interest; you want the syscall entry; timestamp is for exit
>
> .
>

Hi, David,

It's almost what we want, we are eager to see it can work as a callchain option, since it's really a useful
tool in analyzing latency of I/O performance in production case.

--
Thanks,
Yunlong Song



\
 
 \ /
  Last update: 2015-05-06 06:41    [W:0.081 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site