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Message-ID: <20090914185540.GD6045@nowhere>
Date: Mon, 14 Sep 2009 20:55:41 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Masami Hiramatsu <mhiramat@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
lkml <linux-kernel@...r.kernel.org>,
systemtap <systemtap@...rces.redhat.com>,
DLE <dle-develop@...ts.sourceforge.net>,
Jim Keniston <jkenisto@...ibm.com>,
Ananth N Mavinakayanahalli <ananth@...ibm.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>,
"K.Prasad" <prasad@...ux.vnet.ibm.com>,
Lai Jiangshan <laijs@...fujitsu.com>,
Li Zefan <lizf@...fujitsu.com>,
Peter Zijlstra <peterz@...radead.org>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Tom Zanussi <tzanussi@...il.com>
Subject: Re: [PATCH tracing/kprobes 4/7] tracing/kprobes: Add event
profiling support
On Mon, Sep 14, 2009 at 12:54:24PM -0400, Masami Hiramatsu wrote:
>>> I'd like to have a dispatcher function and flags internally :)
>>
>>
>> You mean kprobes that could support multiple probes?
>> That would be a nice solution IMHO...
>
> Yeah, actually kprobes could support multiple probes on the
> same point. But kprobe structure has many extensions which
> kprobe-tracer doesn't need, e.g. post_handler/break_handler,
> opcode, arch sprcific instructions.
> Kretprobe consumes more memories for storing return points :(.
>
> Thus, if we know there are two functions to be called on the
> same probe point, I think it is better to have a dispatcher.
> (Especially, in this case, we can call fixed functions, so
> it's easier way.)
>
Yeah, you could union the post_handler with profile_handler
or something like that.
It depends if kprobes may need one day to support an undeterminate
number of probes.
Also, is the post_handler called at the same location than the normal
probe?
And is a post handler called even if there is no normal handler?
There might be some of such factors that would force you to handle a
lot of corner cases, things that you wouldn't need to worry about
if you just had to maintain a simple rcu list of probes to call.
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