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

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Message-ID: <c62985530907201422i3f18813at7f6028e4be68d48f@mail.gmail.com>
Date:	Mon, 20 Jul 2009 17:22:00 -0400
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	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

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...

Damn, I forgot Masami in the Cc list...
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