Message-ID: <4A6A1775.2050907@redhat.com>
Date: Fri, 24 Jul 2009 16:20:05 -0400
From: Masami Hiramatsu <mhiramat@redhat.com>
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To: =?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?= <fweisbec@gmail.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Thomas Gleixner <tglx@linutronix.de>, Mike Galbraith <efault@gmx.de>,
       Paul Mackerras <paulus@samba.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Lai Jiangshan <laijs@cn.fujitsu.com>, Anton Blanchard <anton@samba.org>,
       Li Zefan <lizf@cn.fujitsu.com>, Zhaolei <zhaolei@cn.fujitsu.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       "K . Prasad" <prasad@linux.vnet.ibm.com>,
       Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware
 	breakpoints
References: <1248109687-7808-1-git-send-email-fweisbec@gmail.com>	 <1248109687-7808-6-git-send-email-fweisbec@gmail.com>	 <1248111537.15751.9341.camel@twins> <c62985530907201422i3f18813at7f6028e4be68d48f@mail.gmail.com>
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Fr?d?ric Weisbecker wrote:
> 2009/7/20, Peter Zijlstra <a.p.zijlstra@chello.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@redhat.com

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