linux-kernel - Re: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware breakpoints

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Message-ID: <4A6A1775.2050907@redhat.com>
Date:	Fri, 24 Jul 2009 16:20:05 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Frédéric Weisbecker <fweisbec@...il.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Anton Blanchard <anton@...ba.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Zhaolei <zhaolei@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"K . Prasad" <prasad@...ux.vnet.ibm.com>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware
 	breakpoints

Frédéric Weisbecker wrote:
> 2009/7/20, Peter Zijlstra <a.p.zijlstra@...llo.nl>:
>> On Mon, 2009-07-20 at 13:08 -0400, Frederic Weisbecker wrote:
>>> This adds the support for kernel hardware breakpoints in perfcounter.
>>> It is added as a new type of software counter and can be defined by
>>> using the counter number 5 and by passsing the address of the
>>> breakpoint to set through the config attribute.
>> This seems to be IP based breakpoints. Are there plans for data based
>> breakpoints as well? In that case we might want to think about the
>> namespace issue, we cannot both call them breakpoint/bp etc.. ;-)
> 
> 
> Nop, by default these breakpoints trigger on READ/WRITE accesses, it's
> meant for data.
> The example in the changelog profiles the bkl accesses, not by tracing
> lock_kernel() or so...but by tracing the kernel_flag spinlock itself.
> 
> So it's the opposite, we may start thinking about naming issues
> against possible future plans
> for IP breakpoint :-)
> 
> But actually for the latter case, I would suggest Kprobe...

Yeah, after kprobes-based event tracer is supported on ftrace,
it is easy to set up IP breakpoints in the kernel.
(maybe, I need to enhance it for perfcounter.)

Thank you,

-- 
Masami Hiramatsu

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

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

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