Re: [PATCH v2] perf tools: Allow passing perf's own pid to '--filter'

[Wangnan (F)]

On 2015/7/7 20:33, Namhyung Kim wrote:
> Hi,
>
> On Tue, Jul 7, 2015 at 12:38 PM, Wang Nan <wangnan0@xxxxxxxxxx> wrote:
> > This patch allows passing perf's own PID to '--filter' by using
> > '$PERFPID'. This should be useful when system-widely capturing
> > tracepoints events.
> >
> > Before this patch, when doing something like:
> >
> >   # perf record -a -e syscalls:sys_enter_write <cmd>
> >
> > One could easily get result like this:
> >
> >   # perf report --stdio
> >   ...
> >   # Overhead  Command  Shared Object       Symbol
> >   # ........  .......  ..................  ....................
> >   #
> >       99.99%  perf     libpthread-2.18.so  [.] __write_nocancel
> >       0.01%   ls       libc-2.18.so        [.] write
> >       0.01%   sshd     libc-2.18.so        [.] write
> >       ...
> >
> > Where most events are generated by perf itself.
> >
> > A shell trick can be done to filter perf itself out:
> >
> >   # cat << EOF > ./tmp
> >   > #!/bin/sh
> >   > exec perf record -e ... --filter="common_pid != \$\$" -a sleep 10
> >   > EOF
> >   # chmod a+x ./tmp
> >   # ./tmp
> >
> > However, doing so is user unfriendly.
> >
> > This patch introduces '$PERFPID' placeholder to perf's filter. Now
> > user is allowed to do the above work with:
> >
> >    # perf record -e ... --filter='common_pid != $PERFPID' -a sleep 10
> Instead, what about adding an option to do the same thing, like
> --exclude-perf or something?

I thought this idea. Please see one of my previous email:

http://lkml.kernel.org/r/559B3CC3.2030503@xxxxxxxxxx

This patch gives user full control of their filters. They can create 
filters like 'common_pid == $PERFPID' to profile perf itself, or use it 
in some complex expressions.

But if most of you like adding new option, I can post a v3 with 
'--exclude-perf' added. Yes, the code of it can be much simpler than 
this patch.

> Thanks,
> Namhyung
>
>
> > This patch adds the variable replacement code to perf_evsel__apply_filter(),
> > before PERF_EVENT_IOC_SET_FILTER ioctl, so not only 'perf record', all
> > subcommands which uses filter can utilize $PERFPID.
> >
> > Andi Kleen sent a similar patch at 2014, but wasn't applied, the
> > reason is not clear.
> >
> > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>


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