linux-kernel - Re: [PATCH RFC] Fix per-task profiling Re: [PATCH] perf: Allow set output buffer for tasks in the same thread group

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Date:	Wed, 27 Apr 2011 10:40:46 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Tim Blechmann <tim@...ngt.org>,
	David Ahern <dsahern@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] Fix per-task profiling Re: [PATCH] perf: Allow set
 output buffer for tasks in the same thread group

On Wed, 2011-04-27 at 04:44 +0800, Arnaldo Carvalho de Melo wrote:
> Em Mon, Apr 25, 2011 at 12:28:33PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Mon, Apr 25, 2011 at 09:40:38PM +0800, Lin Ming escreveu:
> > > On Mon, 2011-04-25 at 01:05 +0800, Peter Zijlstra wrote:
> > > > On Sun, 2011-04-24 at 22:57 +0800, Lin Ming wrote:
> > > > > Currently, kernel only allows an event to redirect its output to other
> > > > > events of the same task.
> 
> > > > > This causes PERF_EVENT_IOC_SET_OUTPUT ioctl fails when an event is
> > > > > trying to redirect its output to other events in the same thread group.
> 
> > > > Which is exactly what it should do, you should never be allowed to
> > > > redirect your events to that of another task, since that other task
> > > > might be running on another CPU.
> 
> > > > The buffer code strictly assumes no concurrency, therefore its either
> > > > one task or one CPU.
> 
> > > Well, this is not the right fix, then the perf tool code need to be
> > > fixed.
>  
> > Yes, I'm working on it.
> 
> Lin, David, Tim, can you please try the two patches attached?
> 
> Tested with:
> 
> [root@...icio ~]# tuna -t 26131 -CP | nl
>   1                      thread       ctxt_switches
>   2    pid SCHED_ rtpri affinity voluntary nonvoluntary             cmd
>   3 26131   OTHER     0      0,1  10814276      2397830 chromium-browse 
>   4  642    OTHER     0      0,1     14688            0 chromium-browse 
>   5  26148  OTHER     0      0,1    713602       115479 chromium-browse 
>   6  26149  OTHER     0      0,1    801958         2262 chromium-browse 
>   7  26150  OTHER     0      0,1   1271128          248 chromium-browse 
>   8  26151  OTHER     0      0,1         3            0 chromium-browse 
>   9  27049  OTHER     0      0,1     36796            9 chromium-browse 
>  10  618    OTHER     0      0,1     14711            0 chromium-browse 
>  11  661    OTHER     0      0,1     14593            0 chromium-browse 
>  12  29048  OTHER     0      0,1     28125            0 chromium-browse 
>  13  26143  OTHER     0      0,1   2202789          781 chromium-browse 
> [root@...icio ~]#
> 
> So 11 threads under pid 26131, then:
> 
> [root@...icio ~]# perf record -F 50000 --pid 26131 
> 
> [root@...icio ~]# grep perf_event /proc/`pidof perf`/maps | nl
>   1 7fa4a2538000-7fa4a25b9000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   2 7fa4a25b9000-7fa4a263a000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   3 7fa4a263a000-7fa4a26bb000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   4 7fa4a26bb000-7fa4a273c000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   5 7fa4a273c000-7fa4a27bd000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   6 7fa4a27bd000-7fa4a283e000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   7 7fa4a283e000-7fa4a28bf000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   8 7fa4a28bf000-7fa4a2940000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>   9 7fa4a2940000-7fa4a29c1000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>  10 7fa4a29c1000-7fa4a2a42000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
>  11 7fa4a2a42000-7fa4a2ac3000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
> [root@...icio ~]#
> 
> 11 mmaps, one per thread since we didn't specify any CPU list, so we need one
> mmap per thread and:
> 
> [root@...icio ~]# perf record -F 50000 --pid 26131 
> ^M
> ^C[ perf record: Woken up 79 times to write data ]
> [ perf record: Captured and wrote 20.614 MB perf.data (~900639 samples) ]
> 
> [root@...icio ~]# perf report -D | grep PERF_RECORD_SAMPLE | cut -d/ -f2 | cut -d: -f1 | sort -n | uniq -c | sort -nr | nl
>      1	 371310 26131
>      2	  96516 26148
>      3	  95694 26149
>      4	  95203 26150
>      5	   7291 26143
>      6	     87 27049
>      7	     76 661
>      8	     60 29048
>      9	     47 618
>     10	     43 642
> [root@...icio ~]#
> 
> Ok, one of the threads, 26151 was quiescent, so no samples there, but all the
> others are there.
> 
> Then, if I specify one CPU:
> 
> [root@...icio ~]# perf record -F 50000 --pid 26131 --cpu 1

Tested and it works OK.

But here is one thing make me confused.
I thought that "--pid" and "--cpu" parameters are not allowed to be used
at the same time. Otherwise, is it a task event or cpu event?

Or does it mean that the event is only monitored when the "task" is
running on the specified "cpu"?

Thanks,
Lin Ming

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