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xen-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: |
"Stephen C. Tweedie" <sct@xxxxxxxxxx> |
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Date: |
Fri, 07 Apr 2006 09:55:43 -0400 |
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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>, okrieg@xxxxxxxxxx, Tristan Gingold <Tristan.Gingold@xxxxxxxx>, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx |
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Fri, 07 Apr 2006 06:57:01 -0700 |
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Hi,
On Wed, 2006-04-05 at 07:07 -0700, Magenheimer, Dan (HP Labs Fort
Collins) wrote:
> I believe ppc has "paravirtualized spinlocks" in their Linux
> kernel
ppc64 does. From include/asm-ppc64/spinlock.h:
/*
* On a system with shared processors (that is, where a physical
* processor is multiplexed between several virtual processors),
* there is no point spinning on a lock if the holder of the lock
* isn't currently scheduled on a physical processor. Instead
* we detect this situation and ask the hypervisor to give the
* rest of our timeslice to the lock holder.
*
* So that we can tell which virtual processor is holding a lock,
* we put 0x80000000 | smp_processor_id() in the lock when it is
* held. Conveniently, we have a word in the paca that holds this
* value.
*/
A quick hack for this which simply did a yield sched_op when it detected
a collision could be done in the same way from a paravirtualised kernel
without any HV changes; but I think it would take extra scheduler help
to do a directed yield to a specific CPU.
--Stephen
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