linux-kernel - Re: [PATCH 3/4] trace: add ability to collect call chain of non-current task.

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Message-ID: <4EEA101C.7060505@gmail.com>
Date:	Thu, 15 Dec 2011 19:19:56 +0400
From:	Andrew Vagin <avagin@...il.com>
To:	Arun Sharma <asharma@...com>
CC:	avagin@...nvz.org, Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 3/4] trace: add ability to collect call chain of non-current
 task.

On 12/15/2011 12:14 AM, Arun Sharma wrote:
>
>
> On 12/9/11 3:07 AM, Andrey Vagin wrote:
>
>>> Attached is an alternative approach that does what you allude to above.
>>
>> * Your method doesn't work for rt scheduler.
>
> This is no worse than sched_stat_{iowait,sleep} which are also CFS 
> specific?
Sorry. You are right. It's the same.
>
>> * It doesn't distinguish blocking time and sleeping time.
>
> Can't we distinguish based on next->state?
It will be "Running". We can distinguish based on block_start of sleep_start
>
>> * This patch does a bit mess between subsystems...
>
> Which subsystems?
sched_switch belongs to scheduler.
sched_stat belongs to sched_fair.

I am not sure, that it's bad. Send this patches in LKML.

>
>>> perf record -agPe sched:sched_switch --filter "delay > 1000000" --
>>> sleep 1
>>
>> Why do you need the option "-a" ?
>>
>
> I'd love to see it work without the -a (so normal users can use it).
>
> I guess I'll need to move the trace_sched_switch() tracepoint to be 
> after perf_event_task_sched_in() in finish_task_switch().
>
>
>>>
>>> allows us to collect a lot less. For some reason, "perf script" shows
>>
>>> the correct delay field, but the sample period still contains 1 (i.e
>>> __perf_count() hint is not working for me).
>>
>> Which kernel do you use? Does it contain "[PATCH] event: don't divide
>> events if it has field period"? It works fine with my kernel...
>>
>
> I was using 3.2-rc2. I picked up the patch you reference above.
>
> # perf report -D | grep SAMPLE.*period:
> 3 1437330416084 0x26d908 [0x250]: PERF_RECORD_SAMPLE(IP, 1): 
> 7276/7806: 0xffffffff8102c0a7 period: 140736819516096 addr: 0
> 3 1437330422290 0x26db58 [0x250]: PERF_RECORD_SAMPLE(IP, 1): 
> 7276/7806: 0xffffffff8102c0a7 period: 140736819516096 addr: 0
> 3 1437330428485 0x26dda8 [0x250]: PERF_RECORD_SAMPLE(IP, 1): 
> 7276/7806: 0xffffffff8102c0a7 period: 140736819516096 addr: 0
>
> # perf script | grep next_comm=test.*delay | head -3
>             test 13070 [023]  1437.320529: sched_switch: 
> prev_comm=kworker/0:1 prev_pid=0 prev_prio=120 prev_state=R ==> 
> next_comm=test next_pid=13070 next_prio=120 delay=1096877
>             test 13070 [023]  1437.320531: sched_switch: 
> prev_comm=kworker/0:1 prev_pid=0 prev_prio=120 prev_state=R ==> 
> next_comm=test next_pid=13070 next_prio=120 delay=1096877
>             test 13070 [023]  1437.320532: sched_switch: 
> prev_comm=kworker/0:1 prev_pid=0 prev_prio=120 prev_state=R ==> 
> next_comm=test next_pid=13070 next_prio=120 delay=1096877
>
> The period still looks bogus i.e. doesn't match delay.

I pushed my tree on github git://github.com/avagin/perf.git. Look at 
branch "arun" https://github.com/avagin/perf/tree/arun

It works for me. You can find output of commands bellow.

# ./perf record -e sched:sched_switch -agP
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.091 MB perf.data (~3954 samples) ]

# ./perf report -D | grep SAMPLE.*period:
1 1539849049077 0x10d78 [0xc8]: PERF_RECORD_SAMPLE(IP, 1): 34/34: 
0xffffffff810527c4 period: 7714488 addr: 0

#./perf script
  kworker/1:2    34 [001]  1539.849049: sched_switch: prev_comm=perf 
prev_pid=2700 prev_prio=120 prev_state=R ==> next_comm=kworker/1:2 
next_pid=34 next_prio=120 delay=7714488
> Thanks for reviewing. I'll clean up some of these issues and post a 
> new patch in a couple of days.
>
>  -Arun
>
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