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

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Date:	Thu, 27 Aug 2009 09:31:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	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 <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
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