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

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Message-ID: <20130425151035.GA26760@redhat.com>
Date:	Thu, 25 Apr 2013 17:10:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Jacob Shin <jacob.shin@....com>, Ingo Molnar <mingo@...hat.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,
	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 04/25, Frederic Weisbecker wrote:
>
> 2013/4/23 Jacob Shin <jacob.shin@....com>:
> > @@ -286,7 +286,10 @@ struct perf_event_attr {
> >                 __u64           config1; /* extension of config */
> >         };
> >         union {
> > -               __u64           bp_len;
> > +               struct {
> > +                       __u32           bp_len;
> > +                       __u32           bp_addr_mask;
> > +               };
>
> Do we need len and mask to work at the same time? I can't think of a
> situation when len and mask mix up together in a useful way to define
> a range.

And it would be nice (I think) if we could simply turn bp_len into
bp_mask. It is already the mask actually, bp_addr should be aligned.

But I do not see how we can do this, so I guess we need another field.

Well. Another option is to extend bp_len. Fortunately HW_BREAKPOINT_LEN_*
match the length, so we can simply allow any 2^n length and amd.c can
translate it into the mask.

Of course, this doesn't allow to use, say, mask=0xF0. But perhaps this
is not really useful?

I dunno. I leave this to you and Jacob ;)

Oleg.

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