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

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Message-ID: <Pine.LNX.4.44L0.0907231555050.3509-100000@iolanthe.rowland.org>
Date:	Thu, 23 Jul 2009 15:56:08 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	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>
Subject: Re: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware
 breakpoints

On Thu, 23 Jul 2009, Peter Zijlstra wrote:

> > Is there a limit to these hardware breakpoints? If so, the software

Certainly there's a limit.  They require hardware resources, after all.

> > counter model is not sufficient, since we assume we can always schedule
> > all software counters. However if you were to add more counters than you
> > have hardware breakpoints you're hosed.
> 
> Do the breakpoints work on virtual or physical addresses?

On x86, hardware breakpoints take virtual addresses.  I don't know 
about other architectures.

Alan Stern

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