linux-kernel - Re: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG

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Message-ID: <4B62F61D.5060203@redhat.com>
Date:	Fri, 29 Jan 2010 09:52:13 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Subject: Re: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG_PREEMPT=y

Ingo Molnar wrote:
> 
> * Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 
>> Disable kprobe booster when CONFIG_PREEMPT=y, because it can't ensure that 
>> all kernel threads preempted on kprobe's boosted slot run out from the slot 
>> even using freeze_processes().
> 
> hm, this really sucks as it makes preemptible kernels perform worse. Is there 
> no better solution?
> 
>> The booster on preemptive kernel will be resumed if synchronize_tasks() or 
>> something like that is introduced.
> 
> such as this one?

Yes, I think this synchronize_tasks(), which just (sleeping) wait until
all currently preempted tasks are wake up and scheduled, can ensure safety.

Thank you,

-- 
Masami Hiramatsu

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

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

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