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


    On 04/26/11 14:44, 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@felicio ~]# 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@felicio ~]#
    >
    > So 11 threads under pid 26131, then:
    >
    > [root@felicio ~]# perf record -F 50000 --pid 26131
    >
    > [root@felicio ~]# 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@felicio ~]#
    >
    > 11 mmaps, one per thread since we didn't specify any CPU list, so we need one
    > mmap per thread and:
    >
    > [root@felicio ~]# 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@felicio ~]# 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@felicio ~]#
    >
    > 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@felicio ~]# perf record -F 50000 --pid 26131 --cpu 1
    > ^C[ perf record: Woken up 1 times to write data ]
    > [ perf record: Captured and wrote 0.680 MB perf.data (~29730 samples) ]
    >
    > [root@felicio ~]# perf report -D | grep PERF_RECORD_SAMPLE | cut -d/ -f2 | cut -d: -f1 | sort -n | uniq -c | sort -nr | nl
    > 1 8444 26131
    > 2 2584 26149
    > 3 2518 26148
    > 4 2324 26150
    > 5 123 26143
    > 6 9 661
    > 7 9 29048
    > [root@felicio ~]#
    >
    > This machine has two cores, so fewer threads appeared on the radar, and:
    >
    > [root@felicio ~]# grep perf_event /proc/`pidof perf`/maps | nl
    > 1 7f484b922000-7f484b9a3000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
    > [root@felicio ~]#
    >
    > Just one mmap, as now we can use just one per-cpu buffer instead of the
    > per-thread needed in the previous case.
    >
    > For global profiling:
    >
    > [root@felicio ~]# perf record -F 50000 -a
    > ^C[ perf record: Woken up 26 times to write data ]
    > [ perf record: Captured and wrote 7.128 MB perf.data (~311412 samples) ]
    >
    > [root@felicio ~]# grep perf_event /proc/`pidof perf`/maps | nl
    > 1 7fb49b435000-7fb49b4b6000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
    > 2 7fb49b4b6000-7fb49b537000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
    > [root@felicio ~]#
    >
    > It uses per-cpu buffers.
    >
    > For just one thread:
    >
    > [root@felicio ~]# perf record -F 50000 --tid 26148
    > ^C[ perf record: Woken up 2 times to write data ]
    > [ perf record: Captured and wrote 0.330 MB perf.data (~14426 samples) ]
    >
    > [root@felicio ~]# perf report -D | grep PERF_RECORD_SAMPLE | cut -d/ -f2 | cut -d: -f1 | sort -n | uniq -c | sort -nr | nl
    > 1 9969 26148
    > [root@felicio ~]#
    >
    > [root@felicio ~]# grep perf_event /proc/`pidof perf`/maps | nl
    > 1 7f286a51b000-7f286a59c000 rwxs 00000000 00:09 4064 anon_inode:[perf_event]
    > [root@felicio ~]#
    >
    > Can you guys please test it and provide Tested-by and/or Acked-by?
    >
    > Thanks,
    >
    > - Arnaldo

    Worked for me (KVM process).

    Tested-by: David Ahern dsahern@gmail.com


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