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Date: Mon, 6 Jul 2015 12:37:02 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>, a.p.zijlstra@chello.nl, mingo@redhat.com,
        jolsa@kernel.org, peterz@infradead.org, namhyung@kernel.org,
        kan.liang@intel.com, adrian.hunter@intel.com, ak@linux.intel.com,
        cody@linux.vnet.ibm.com, jacob.w.shin@gmail.com, standby24x7@gmail.com,
        lizefan@huawei.com, yunlong.song@huawei.com,
        linux-kernel@vger.kernel.org, pi3orama@163.com
Subject: Re: [PATCH] perf record: Allow passing perf's own pid to '--filter'
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On Mon, 6 Jul 2015 10:56:50 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Em Mon, Jul 06, 2015 at 04:17:31AM +0000, Wang Nan escreveu:
> > This patch allows passing perf's own PID to '--filter' by using
> > '@PERFPID'. This should be useful when system-widely capturing
> > tracepoints events.
> 
> Steven, does filters have any special meaning for @?

Not as of yet.


>  
> > Before this patch, when doing something like:
> > 
> >  # perf record -a -e syscalls:sys_enter_write <cmd>
> > 
> > One could easily get result like this:
> > 
> >  # /tmp/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 '--filter' options. Now
> > user is allowed to the above work with:
> > 
> >   # perf record -e ... --filter="common_pid != @PERFPID' sleep 10

What about using '$' instead. That is more common to shell scripts of
being a variable.

-- Steve

> > 
> > Signed-off-by: Wang Nan <wangnan0@huawei.com>
> > ---
> >  tools/perf/Documentation/perf-record.txt |  1 +
> 
> <SNIP>
> 
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