linux-kernel - Re: [PATCH 2/2] perf record: Add --dry-run option to check cmdline options

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Date:	Tue, 21 Jun 2016 14:12:38 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	"Arnaldo Carvalho de Melo" <acme@...hat.com>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	David Ahern <dsahern@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH 2/2] perf record: Add --dry-run option to check cmdline
 options



On 2016/6/21 0:22, Alexei Starovoitov wrote:
> On Mon, Jun 20, 2016 at 11:38:18AM -0300, Arnaldo Carvalho de Melo wrote:
>> Em Mon, Jun 20, 2016 at 11:29:13AM +0800, Wangnan (F) escreveu:
>>> On 2016/6/17 0:48, Arnaldo Carvalho de Melo wrote:
>>>> Em Thu, Jun 16, 2016 at 08:02:41AM +0000, Wang Nan escreveu:
>>>>> With '--dry-run', 'perf record' doesn't do reall recording. Combine with
>>>>> llvm.dump-obj option, --dry-run can be used to help compile BPF objects for
>>>>> embedded platform.
>>>> So these are nice and have value, but can we have a subcommand to do all
>>>> this with an expressive name, Something like:
>>>>    perf bpfcc foo.c -o foo
>>>> or shorter:
>>>>    perf bcc foo.c -o foo
>>>> Just like one would use gcc or some other compiler to generate something
>>>> for later use?
>>> I'll try it today. I thought a subcommand require a bigger feature,
>>> and wrapping clang is not big enough.
>> Not really, we may have as many as we like, given that they provide
>> something useful, like I think is the case here.
>>
>> Having to edit ~/.perfconfig, create a new section, a variable in it
>> with a boolean value (at first, just reading the changeset comment, I
>> thought I had to provide a directory where to store the objects
>> "dumped"), to then use a tool to record a .c event, but not recording
>> (use dry-run, which is useful to test the command line, etc), to then
>> get, on the current directory, the end result looked to me a convoluted
>> way to ask perf to compile the given .c file into a .o for later use.
>>
>> Doing:
>>
>> 	perf bcc -c foo.c
>>
>> Looks so much simpler and similar to an existing compile source code
>> into object file workflow (gcc's, any C compiler) that I think it would
>> fit in the workflow being discussed really nicely.
> I'm hopeful that eventually we'll be able merge iovisor/bcc project
> with perf, so would be good to reserve 'perf bcc' command for that
> future use. Also picking a different name for compiling would be less
> confusing to users who already familiar with bcc. Instead we can use:
> perf bpfcc foo.c -o foo.o
> perf cc foo.c
> perf compile foo.c
>

I think finally we should make perf independent with LLVM runtime.
I suggest 'perf bpf' subcommand to deal with all BPF related things,
include compiling, configuration and potential cache.

Thank you.