Re: [PATCH 1/1] perf,tools: add time out to force stop endless mmap processing

[David Ahern]

On 6/12/15 11:05 AM, Liang, Kan wrote:
> > On 6/12/15 8:42 AM, Liang, Kan wrote:
> > > > On 6/11/15 12:47 PM, Andi Kleen wrote:
> > > > > > Can you elaborate on an example? I don't see how this can happen
> > > > > > reading a maps file. And it does not read maps for all threads only
> > > > > > thread group leaders.
> > > > >
> > > > > This is with a stress test case that generates lots of small
> > > > > mappings at very high speed and frees them again. So the maps file
> > > > > keeps changing faster than the proc reader can keep it and it can
> > > > > end up with a live lock.
> > > >
> > > > Can you pass it along? I'd like to see how the task_diag proposal handles
> > it.
> > > > https://github.com/dsahern/linux/commits/task_diag-wip
> > >
> > > Hi David,
> > >
> > > I tried the task_diag on my platform, but it shows error message when
> > > I run perf top. " Message handling failed: rc -1, errno 25".
> > > And it looks perf top failed to get maps information.
> >
> > Not surprising; it's only half-baked. Can you try perf-record? So far that is
> > the only one I have tested.
>
> Perf record cannot reproduce the infinite loop which found in perf top.
> But we can observe that synthesized threads took very long time in perf record.
>
> According to test result as below, current perf cost 13s to read the maps,
> while task_diag cost 14s to synthesized thread.
> (Note: The time will increase with the test run.)
>
> So it looks task_diag doesn't help on this issue.
>
> [perf]$ sudo ./perf record -e instructions:pp --pid 14560
> Reading /proc/14560/maps cost 13.12690599 s
> ^C[ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.108 MB perf.data (2783 samples) ]

so perf was able to read the proc file?

> [perf]$ sudo ./perf_task_diag record -e instructions:pp --pid 14560
> synthesized threads took 14.435450 sec
> ^C[ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.035 MB perf.data (885 samples) ]
>
>
> > Also, while running that kernel you can build the test programs under
> > tools/testing/selftests/task_diag/ and try task_diag_all. I am away from my
> > dev box at the moment. As I recall you will want to try 'task_diag_all o $pid'
> > or 'task_diag_all a'
> Neither options work on my platform.
>
> [task_diag]$ sudo ./task_diag_all a
> Unable to receive message: Operation not supported
> [task_diag]$ sudo ./task_diag_all o 14751
> Unable to receive message: Operation not supported

Are you sure task_diag is enabled? There is an option under General I 
believe:
config TASK_DIAG
        bool "Export task/process properties through netlink"
        depends on NET && TASKSTATS
        default n
        help
          Export selected properties for tasks/processes through the
          generic netlink interface. Unlike the proc file system, task_diag
          returns information in a binary format, allows to specify which
          information are required.

          Say N if unsure.

David

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