linux-kernel - Re: [PATCH tracing/kprobes 4/7] tracing/kprobes: Add event profiling support

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Date:	Fri, 11 Sep 2009 12:22:16 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.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

Frederic Weisbecker wrote:
>> +static int probe_profile_enable(struct ftrace_event_call *call)
>> +{
>> +	struct trace_probe *tp = (struct trace_probe *)call->data;
>> +
>> +	if (atomic_inc_return(&call->profile_count))
>> +		return 0;
>> +
>> +	if (probe_is_return(tp)) {
>> +		tp->rp.handler = kretprobe_profile_func;
>> +		return enable_kretprobe(&tp->rp);
>> +	} else {
>> +		tp->rp.kp.pre_handler = kprobe_profile_func;
>> +		return enable_kprobe(&tp->rp.kp);
>> +	}
>> +}
>
>
>
> May be I misunderstood but it seems that concurrent uses of
> ftrace and perf would really mess up the result, as one would
> overwrite the handler of the other.
>
> Even though it's hard to imagine one using both at the same
> time on the same probe, but still...

Oops, it's my misunderstanding. I thought those are exclusively
enabled each other.

> Is it possible to have two kprobes having the exact same
> properties? (pointing to the same address, having the same
> probe handlers, etc...)
>
> Another solution would be to allow kprobes to have multiple
> handlers.

It could be to have multiple kprobes on same point, but I think
it's waste of the memory and time in this case.

I'd like to have a dispatcher function and flags internally :)

Thank you,

-- 
Masami Hiramatsu

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

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

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