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xen-devel
Re: [Xen-users] Re: [Xen-devel] VMX Hardware
On 14 Aug 2005, at 13:23, Mogens Valentin wrote:
I assume by VMX, you're talking about cpu/hardware with HW-support for
virtualisation, i.e. Intels Vanderbilt Technology (VT) and AMD'
Pacifica. If so, it's clear to me that AMD will be leading, because of
it's onchip memory controller, and hence reduced needs for software
support to do the page switching, for which Intel needs quite a lot of
software to emulate.
Not sure what you mean. Both technologies require the hypervisor to
maintain shadow page tables. SVM (Pacifica) does have the advantage of
a tagged TLB, so avoiding TLB flushes when switching between guest mode
and hypervisor mode, and between guests, but we have no measurements so
estimates of relative performance are pure conjecture.
However, I'm not sufficiently familiar with Xen on this topic (just
getting started). What I've read is that Xen won't benefit from or
even use those HW-enabled mechanisms.
Someone pls. correct me if I'm wrong here - I'd very much like to be
wrong. Would be a pity not to take advantage of such mechanisms, IMHO.
Xen will use VT and SVM to run unmodified operating systems. This will
be useful for virtualising legacy system installations, and for
supporting OSes where the source is not freely available.
Xen already has VT support, and I expect that SVM will also be
supported by the end of the year. Hardware won't be generally available
before then anyway.
-- Keir
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