linux-kernel - Re: [PATCH -tip perf/probes 00/10] x86 insn decoder bugfixes and perf-probe syntax changes

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Message-ID: <20091103073236.GB19928@elte.hu>
Date:	Tue, 3 Nov 2009 08:32:36 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frédéric 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>,
	"H. Peter Anvin" <hpa@...or.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>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip perf/probes 00/10] x86 insn decoder bugfixes and
	perf-probe syntax changes


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

> Masami Hiramatsu wrote:
>> Masami Hiramatsu wrote:
>>> Ingo Molnar wrote:
>>>> What we want here is two fold:
>>>>
>>>>     - enable kprobes event support when perf events is enabled and kprobes
>>>>       is enabled. We dont want another config option for it.
>>>
>>> Sure, at least that combination should enable kprobe-tracer forcibly.
>>
>> Hmm, someone may not want to enables kprobe-tracer. Perhaps,
>> "default y if (EVENT_PROFILE)" is enough, isn't it?
>
> Oops, this causes recursive dependency error :-(
>
> kernel/trace/Kconfig:90:error: found recursive dependency: TRACING ->
> EVENT_TRACING -> EVENT_PROFILE -> KPROBE_TRACER -> GENERIC_TRACER -> TRACING

This dependency problem can be resolved by simply making it 'default y' 
- the option itself depends on KPROBES already, which is default-off - 
so no need to also make it depend on EVENT_PROFILE.

btw., it would be nice to re-name it to 'KPROBE_EVENTS'. If the probe 
point is used as a count - like in the __switch_to example i cited - 
there's no tracing going on at all.

	Ingo
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