linux-kernel - Re: [PATCH -tip 0/9] perf-probe updates

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Date:	Tue, 1 Dec 2009 08:29:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jim Keniston <jkenisto@...ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jason Baron <jbaron@...hat.com>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip 0/9] perf-probe updates

* Masami Hiramatsu <mhiramat@...hat.com> wrote:

> Hi,
> 
> Here are bugfixes and updates for perf-probe and kprobe-tracer. I've 
> fixed some minor bugs and added --list option and simple probe naming.

Applied, thanks Masami!

> TODO:
>  - Support build-id checking.
>  - Support --del option to remove probes.
>  - Support --line option to show which lines user can probe.
>  - Support lazy string matching.

ok, cool!

One other small detail i noticed wrt. probe naming. Right now if we 
insert a single probe into a function it gets named schedule_0:

 # perf probe schedule
 Could not open vmlinux/module file. Try to use symbols.
 Added new event: p:probe/schedule_0 schedule+0

the next one gets named schedule_1, schedule_2, etc.

It would be nice to special-case the first one and name it 'schedule'. 
Most of the time people insert a single probe into a function, so the _0 
postfix is extra and in most cases unnecessary typing for them.

Another small detail is that i dont think we should emit this line:

 Could not open vmlinux/module file. Try to use symbols.

when we can create a probe successfully - it's just unnecessary noise, 
the user does not care how we pulled it off, as long as we were able to 
get a reliable symbol address and the insertion worked fine.

A third detail is this line:

 Added new event: p:probe/schedule_0 schedule+0

If that is pasted to perf stat directly it wont work because the syntax 
is probe:schedule_0. So i'd suggest to print something like:

 Added new event: probe/schedule_0 (on schedule+0)

Perhaps even print another line:

  You can now use it on all perf tools, such as:

    perf probe -e probe/schedule_0 -a sleep 1
    perf record -e probe/schedule_0 -a sleep 1

... to show people how to make use of it.

Thanks,

	Ingo
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