Re: [perfmon2] Counting for child threads

[Stephane E. <er...@go...>]

Hi,

On Fri, Apr 24, 2015 at 9:33 PM, Yunqi Zhang <zha...@gm...>
wrote:

> Hi all,
>
> I'm trying to use libpfm to collect performance counter data for some
> multi-threaded applications. I would like to aggregate the data for all the
> child threads under the same process. I found that the "inherit" flag does
> not work for existing children threads as suggested by perf_event_open
> <http://man7.org/linux/man-pages/man2/perf_event_open.2.html>.
>
>        *inherit*
>               The *inherit* bit specifies that this counter should count
>               events of child tasks as well as the task specified.  This
>               applies only to new children, not to any existing children at
>               the time the counter is created (nor to any new children of
>               existing children).
>
> However, it seems to me that the tool perf stat
> <https://perf.wiki.kernel.org/index.php/Main_Page> that comes with Linux
> kernel works just fine in this case, which aggregates the counter data for
> all the child threads even when they already exist.
>
> I was wondering how I can use libpfm to achieve the same purpose, or how perf
> stat implements this functionality.
>
> libpfm4 does not make the perf_event_open() syscall for you. This is still
under the control
of your app. Therefore, you can set the perf_event_attr->inherit flag in
the struct after you've called
libpfm4 and before you call perf_event_open().

You can look at perf_examples/task.c for an example.


> Thank you!
>
> Yunqi
>
>
>
>
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