linux-kernel - Re: [RFC PATCH v3 00/37] perf tools: introduce 'perf bpf' command to load eBPF programs.

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Message-ID: <20150520003052.GE22713@sejong>
Date:	Wed, 20 May 2015 09:30:52 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Alexei Starovoitov <ast@...mgrid.com>,
	Wang Nan <wangnan0@...wei.com>, paulus@...ba.org,
	a.p.zijlstra@...llo.nl, mingo@...hat.com, jolsa@...nel.org,
	dsahern@...il.com, daniel@...earbox.net, brendan.d.gregg@...il.com,
	masami.hiramatsu.pt@...achi.com, lizefan@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [RFC PATCH v3 00/37] perf tools: introduce 'perf bpf' command to
 load eBPF programs.

On Tue, May 19, 2015 at 06:10:33PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, May 19, 2015 at 01:46:10PM -0700, Alexei Starovoitov escreveu:
> > On 5/19/15 9:40 AM, Arnaldo Carvalho de Melo wrote:
> > >Em Wed, May 20, 2015 at 01:04:48AM +0900, Namhyung Kim escreveu:
> > >>If we go with 'perf record' rather than 'perf bpf record', I agree
> > >>that --event option is more natural than --filter.  The --event option
> > >>says that it will record - or enable, at least - a (kprobe) event for
> > >>bpf programs in it and then do something with it. :)
> > >>
> > >>Maybe something like this?
> > >>
> > >>   perf record --event bpf:/path/to/object
> > >
> > >The syntax maybe one of many, say if it sees a ".o" suffix in the even
> > >name, look if the provided event name is a file and if this file has the
> > >ELF header, whatever.
> > 
> > agree. 'bpf:' prefix is redundant.
> 
> I would say unnecessarily exposing an implementation detail :-)
> 
> > To me the following syntax is fine:
> > perf record --event bpf_file.o
> 
> Agreed, for something pre-compiled.
> 
> > In the future it can support automatically:
> > perf record --event bpf_file.c
> 
> Right, to compile it, then use the resulting bpf_file.o just like in the
> first case, then, on another patch, cache it and next time just check
> that the contents of the file hasn't changed, so the .o file can be
> used, i.e. ccache like stuff.
>  
> > Wang, thoughts?
> > 
> > >>Oh, this looks like an interesting approach.. are you saying something
> > >>like below?
> > >
> > >No, those are way too many steps :-)
> > >
> > >What 'perf script' does? Right now you can ask for a script to run and
> > >it will both start 'perf record' with the proper events, and then
> > >"immediately" consume it, piping the output of the 'record' "script" to
> > >the consumer, that is 'perf script' itself running an interpreter, perl
> > >or python.
> > 
> > if you're proposing to do something like:
> > perf script bpf_file.c
> > that will do event creation, filtering, aggregation, reporting
> > and printing results, then it's fine.
> > This is pretty much what I thought 'perf bpf run' will do.
> 
> Agreed, that is what I think should be done, parts of what is in
> bpf.file.c are related to the data collection, some are for filtering,
> and parts are for reporting, etc.

Looks great! :)

> 
> This all should use infrastructure in perf for symbol resolving,
> callcahins, etc.

But then we need to stabilize libperf APIs IMHO. :)

Thanks,
Namhyung
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