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Re: [Xen-devel] [PATCH] Export Multicore information

To: "Kamble, Nitin A" <nitin.a.kamble@xxxxxxxxx>, John Levon <levon@xxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Export Multicore information
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 12 Dec 2006 07:38:49 +0000
Cc: "Yu, Wilfred" <wilfred.yu@xxxxxxxxx>, Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, Xen devel list <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Yang, Fred" <fred.yang@xxxxxxxxx>, "Mallick, Asit K" <asit.k.mallick@xxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>
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On 12/12/06 12:26 am, "Kamble, Nitin A" <nitin.a.kamble@xxxxxxxxx> wrote:

>    Thanks for your comments. The situation is, dom0 may not see all the
> processors in the system. Only hyper visor is capable of seeing all. I
> would let tools/apps on dom0 to see information about CPUs assigned to
> dom0, not the whole set available in the system. So it is necessary to
> have a hyper visor specific interface, and in my opinion xm is the best
> choice for that.

A strong argument against 'xm cacheinfo' and the required extra hypercall is
that x86 cache hierarchies are always symmetric, to the best of my
knowledge. So it does not matter which CPU dom0 happens to interrogate for
cache info -- the information can be extrapolated to all other CPUs in the
system. So the admin can run one of the many little tools that can be
downloaded and that dump out interesting CPUID information. The physical CPU
topology hypercall (i.e., the smaller half of your patch) is more
interesting to me.

 -- Keir



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