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xen-ia64-devel
Re: [Xen-devel] Does dom0 see all physical processors? (RE:[Xen-ia64-dev
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To: |
"Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx> |
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Subject: |
Re: [Xen-devel] Does dom0 see all physical processors? (RE:[Xen-ia64-devel] SAL INFO virtualization) |
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From: |
Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> |
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Date: |
Wed, 5 Apr 2006 15:20:40 +0100 |
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Cc: |
Jimi Xenidis <jimix@xxxxxxxxxxxxxx>, Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, "Tian, Kevin" <kevin.tian@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Tristan Gingold <Tristan.Gingold@xxxxxxxx>, okrieg@xxxxxxxxxx, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx |
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Wed, 05 Apr 2006 07:20:38 -0700 |
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On 5 Apr 2006, at 15:07, Magenheimer, Dan (HP Labs Fort Collins) wrote:
I believe ppc has "paravirtualized spinlocks" in their Linux
kernel, though even this won't necessarily help with a poorly
written SMP application.
No data, admittedly, but perhaps our good buddies at
Watson could comment?
IBM did some investigation into this a while back. The conclusion then
was that, even in a microbenchmark somewhat contrived to try and
indicate 'worst case' spinlock behaviour, the benefit of smarter
spinlocks was negligible. Maybe the benchmark was bad, maybe there are
other pathological worst cases out there that the benchmark did not
represent, or maybe the smart spinlocks should have been smarter.
Whatever: the numbers we have so far do not indicate that there's a
problem to be solved, and these potential multi-processor optimisations
have to be empirically driven because intuition is so frequently off
the mark.
-- Keir
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