linux-kernel - Re: [RFC] perf script: callchain handling is not useful

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Date:   Wed, 29 Aug 2018 10:54:40 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC] perf script: callchain handling is not useful

Em Tue, Aug 28, 2018 at 07:41:31PM -0700, Stephane Eranian escreveu:
> Hi,
> 
> I am doing the following simple collection with callchain and load profiling:
> 
> $ perf record -g -d -e cpu/event=0xd0,umask=0x81/pp  my_test_program
> 
> But when I type:
> $ perf script -F ip,addr
> ffff9d4821346878
>         ffffffff9d58df25
>         ffffffff9d58e054
>         ffffffff9d5965bb
>         ffffffff9d640650
>         ffffffff9d697d06
>         ffffffff9d63ec60
>         ffffffff9d640322
>         ffffffff9d64070c
>         ffffffff9d455a60
>                   7030c7
> 
> ffff9d4638ba84a0
>         ffffffff9d5df447
>         ffffffff9d5eaf4a
>         ffffffff9d63e165
>         ffffffff9d63e439
>         ffffffff9d697d98
>         ffffffff9d63ec60
>         ffffffff9d640322
>         ffffffff9d64070c
>         ffffffff9d455a60
>                   7030c7
> I also see the callchain and it is not clear which is the IP. Further
> more parsing becomes more difficult because of multiple lines per
> sample. I understand that multiline is likely because of
> symbolization. But if I don't want symbolization, it should be
> possible to print all in one line.

Humm, to have this not break possibly existing scripts, perhaps we can
have something like:

  $ perf script -F ip,-callchain,addr

?

And if asked explicitely for the callchain, then it gets added in the
same line?

- Arnaldo


> The current output is not very useful. You expect perf script to give
> you one line per sample and only what you want. Callchain != IP.
> 
> I think the following should happen:
>   - do not print callchain when asked for the IP. Create a callchain filter.
>   - print callchain on the same line, much like what is done for brstack
> 
> It is not clear to me why callchain and ip were lumped together.
> Any opinion on my proposal?
> Thanks.