linux-kernel - Re: [PATCH 08/18] tracing: Add kprobe-based event tracer

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Date:	Thu, 27 Aug 2009 11:38:13 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jason Baron <jbaron@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Przemys??aw Pawe??czyk <przemyslaw@...elczyk.it>,
	Roland McGrath <roland@...hat.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: [PATCH 08/18] tracing: Add kprobe-based event tracer

Frederic Weisbecker wrote:
> On Thu, Aug 27, 2009 at 09:31:39AM +0200, Ingo Molnar wrote:
>>
>> * Frederic Weisbecker<fweisbec@...il.com>  wrote:
>>
>>> From: Masami Hiramatsu<mhiramat@...hat.com>
>>>
>>> Add kprobes-based event tracer on ftrace.
>>>
>>> This tracer is similar to the events tracer which is based on
>>> Tracepoint infrastructure. Instead of Tracepoint, this tracer is
>>> based on kprobes (kprobe and kretprobe). It probes anywhere where
>>> kprobes can probe(this
>>>   means, all functions body except for __kprobes functions).
>>>
>>> Similar to the events tracer, this tracer doesn't need to be
>>> activated via current_tracer, instead of that, just set probe
>>> points via /sys/kernel/debug/tracing/kprobe_events. And you can
>>> set filters on each probe events via
>>> /sys/kernel/debug/tracing/events/kprobes/<EVENT>/filter.
>>
>> ok, one observation here: this should seemlessly merge into
>> /debug/tracing/events/ and provide a record format descriptor in
>> 'format' to allow the automated fetching of the results of the
>> probe. The PERF_SAMPLE_RAW gateway should work as well.
>>
>> That way tooling that knows about /debug/tracing/events/ will
>> automatically work with kprobes events as well. We can profile based
>> on kprobes, etc. etc.
>>
>> The _setting_ of the probe is still a separate channel - but if
>> existing installed probes are merged into existing tooling that's a
>> big step forward in terms of utility.
>>
>> 	Ingo
>
>
> It does already :)
>
> But I've split out this patch that initially embeded the documentation.
> If you look at the 9/10 patch, you can see how look like the format
> files for kprobes.

As far as I've tested, it just requires two changes for perf-tools.
- Support CONFIG_PROFILE_EVENT(profile_enable/disable) on kprobe-tracer.
- Ignore 'alias' tag(which is a special tag in kprobes event) while
   parsing format file.

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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