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

["Wangnan (F)" <wangnan0@huawei.com>]

On 2015/7/7 20:33, Namhyung Kim wrote:
> Hi,
>
> On Tue, Jul 7, 2015 at 12:38 PM, Wang Nan <wangnan0@huawei.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?

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

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

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@huawei.com>