Re: [Xen-devel] Architectural question: How to put BTS and PEBS

To:	Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] Architectural question: How to put BTS and PEBS in Xen
From:	Keir Fraser <keir.xen@xxxxxxxxx>
Date:	Tue, 27 Sep 2011 06:24:51 -0700
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On 27/09/2011 02:51, "Dietmar Hahn" <dietmar.hahn@xxxxxxxxxxxxxx> wrote:

> Hi list,
> 
> I'm on the way to coding the virtualisation of BTS (Branch Trace Store) and
> later PEBS support for Intel CPU's in Xen.
> 
> As some aspects overlap with the PMU (Performance Management Unit) I used the
> existing infrastructure of the VPMU stuff to do some coding and tests.
> But currently this infrastructure is only switched on with a 'vpmu' boot flag
> in the  hypervisor.
> As reminder this flag was introduced because of an inexplicable behaviour of
> the Nehalem CPUs while using the performance counters which could lead to an
> endless interrupt loop (see check_pmc_quirk()).
> 
> As currently no one else than we seem to use/need this feature for simplicity
> I would move the BTS code complete to the VPMU environment and therfore it
> would only be usable when using the 'vpmu' flag on boot.

It sounds quite sensible to me.

 -- Keir

> Any advices would be welcome!
> 
> Thanks.
> Dietmar.
> 



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Re: [Xen-devel] Architectural question: How to put BTS and PEBS in Xen