linux-kernel - Re: [PATCH] perf record: Support custom vmlinux path

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Date:	Tue, 17 Nov 2015 09:42:24 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	He Kuang <hekuang@...wei.com>, Wang Nan <wangnan0@...wei.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Alexei Starovoitov <ast@...nel.org>, lizefan@...wei.com,
	pi3orama@....com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf record: Support custom vmlinux path

Em Tue, Nov 17, 2015 at 09:33:40AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Nov 17, 2015 at 09:44:44AM +0000, Wang Nan escreveu:
> 
> Thanks, applying.

I take that back, I think this is questionable, we should instead always
have the --vmlinux option, and when the feature it deals with is not
built in, warn the user about it, something like:

  #  perf record --vmlinux /a/b/c ...
  WARNING: --vmlinux being ignored, as BPF prologue not built-in...
  <output that can be produced while ignoring --vmlinux>

And please consider that for other options that are surrounded by ifdefs
related to the eBPF support, there are a few more, clang related.

Also this isn't updating the perf-record man page, please do so and
please put this in a separate section for BPF related options, something
like:

--------------------

BPF:

These options can be used when BPF support is built-in.

...

---------------------

This way the user gets to know that the tool can be used with BPF while
reading its documentation and if they decide to try it, then the
warnings will be presented if the feature is not built-in.

- Arnaldo
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