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Re: [perfmon] Re: perfmon2 TODO list (4/4)
- From: Stephane Eranian <eranian at hpl dot hp dot com>
- To: William Cohen <wcohen at redhat dot com>
- Cc: "Frank Ch. Eigler" <fche at redhat dot com>, perfmon at napali dot hpl dot hp dot com, systemtap at sources dot redhat dot com
- Date: Tue, 18 Apr 2006 01:38:57 -0700
- Subject: Re: [perfmon] Re: perfmon2 TODO list (4/4)
- Address: HP Labs, 1U-17, 1501 Page Mill road, Palo Alto, CA 94304, USA.
- E-mail: eranian@hpl.hp.com
- Organisation: HP Labs Palo Alto
- References: <20060412215747.GJ29245@frankl.hpl.hp.com> <20060412220659.GL29245@frankl.hpl.hp.com> <20060412221256.GM29245@frankl.hpl.hp.com> <200604131201.59232.kevcorry@us.ibm.com> <20060413200223.GD30718@frankl.hpl.hp.com> <20060413202211.GF22490@redhat.com> <20060413215544.GH30718@frankl.hpl.hp.com> <20060413222251.GI22490@redhat.com> <20060413222338.GA31071@frankl.hpl.hp.com> <44439EA9.5090107@redhat.com>
- Reply-to: eranian at hpl dot hp dot com
Will,
On Mon, Apr 17, 2006 at 09:56:57AM -0400, William Cohen wrote:
> Stephane Eranian wrote:
> >Frank,
> >
> >On Thu, Apr 13, 2006 at 06:22:51PM -0400, Frank Ch. Eigler wrote:
> >
> >>>I have another question related maybe more to kprobes and how the
> >>>intercept is done: breakpoints, code rewriting. If you use
> >>>breakpoints, then I wonder how this works in SMP machines. Do you
> >>>intervene on each CPU?
> >>
> >>That's right: as each CPU trips across a breakpoint, they are made to
> >>run our handler, then single-step across the original instruction,
> >>then resume. It's a multi-step process described in kprobes
> >>documentation. From systemtap's point of view, it's a black box.
> >>
> >
> >So you are saying that kprobes takes care of programming the debug
> >registers on all CPUs if necessary.
> >
>
> Kprobe uses breakpoint instructions, so the breakpoint registers on the
> processor are not currently being used. Thus, a breakpoint instruction
> is placed at the location where the probe is desired and the processor's
> debugging registers are not touch by kprobes.
>
> There has been some discussion for SystemTap producing probes that use
> the processors debug hardware to watch for accesses to specific memory
> locations.
>
So from what you are saying neither kprobes nor systemap uses IPI for any setup/tear
down at this point. Is that right?
--
-Stephane