linux-kernel - Re: [PATCH V2 1/4] perf: Add hardware breakpoint address mask

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Date:	Tue, 23 Apr 2013 09:40:57 -0500
From:	Jacob Shin <jacob.shin@....com>
To:	Will Deacon <will.deacon@....com>
CC:	Ingo Molnar <mingo@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/4] perf: Add hardware breakpoint address mask

On Tue, Apr 23, 2013 at 09:34:23AM -0500, Jacob Shin wrote:
> On Tue, Apr 23, 2013 at 10:54:37AM +0100, Will Deacon wrote:
> > Hi Jacob,
> > 
> > On Tue, Apr 23, 2013 at 08:57:02AM +0100, Jacob Shin wrote:
> > > Some architectures (for us, AMD Family 16h) allow for "don't care" bit
> > > mask to further qualify a hardware breakpoint address, in order to
> > > trap on range of addresses. Update perf uapi to add bp_addr_mask field.
> > 
> > arm and arm64 have a similar feature to this, whereby we currently have to
> > translate the bp_len field into a mask, which is all the hardware
> > understands. Unlike what you describe, our mask indicates the bytes we *are*
> > interested in, but I think we could make use of the same functionality that
> > you're introducing here.
> > 
> > There are some funky restrictions on the alignment of the base address, but
> > we can detect those and tell userspace where to go if it tries any funny
> > stuff.
> > 
> > Can you see a problem if I simply invert the mask?
> 
> Hi,
> 
> That's great! No, I don't see a problem at all.
> 
> I guess now it can be debated if the mask coming in from userland should
> be include or exclude mask. But I think exclude makes syntax easier:
> 
> To count writes to [0x1000 ~ 0x1010)
> 
> Include mask (my current patchset):
  ^^^^^^^
  Exclude (I mean ..)
> 
>   perf stat -e mem:0x1000/0xf:w a.out
> 
> Exclude mask:
  ^^^^^^^
  Include
> 
>   perf stat -e mem:0x1000/0xfff0:w a.out
> 
> Thanks!

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