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

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Date:	Tue, 7 Jul 2015 21:33:02 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Liang, Kan" <kan.liang@...el.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <ak@...ux.intel.com>, jacob.w.shin@...il.com,
	standby24x7@...il.com, Li Zefan <lizefan@...wei.com>,
	yunlong.song@...wei.com, Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	pi3orama@....com
Subject: Re: [PATCH v2] perf tools: Allow passing perf's own pid to '--filter'

Hi,

On Tue, Jul 7, 2015 at 12:38 PM, Wang Nan <wangnan0@...wei.com> 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?

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@...wei.com>
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