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xen-devel
[Xen-devel] Re: CPU scheduling of domains and vcpus
On 21/04/08 18:56 +0100, Samuel Thibault wrote:
> Hello,
>
> Nauman Rafique, le Mon 21 Apr 2008 13:52:21 -0400, a écrit :
> > In fact, wasted cycles can probably be avoided by doing opportunisitic
> > gang scheduling (i.e. gang schedule, unless there would be wasted
> > cycles)
>
> How do you detect that there would be wasted cycles?
The only way is for a very self-aware guest to use a paravirtual
feature to give a hint to the scheduler.
Which is also the way to solve the original problem: the
paravirtualized guest can provide a hint to the scheduler that it is
holding a contended lock.
Alternatively, the scheduler can notify the guest that it is about to
be preempted by the hypervisor and now would be a good time to sleep
before gaining a contended spinlock.
In either case lock contention within a multi-vcpu guest is probably
not as bad a problem as the various solutions cause.
If a workload is suffering so much, give it multiple vcpus that are
mapped 1:1 to physical cpus.
Mike
--
Mike D. Day
IBM LTC
Cell: 919 412-3900
Sametime: ncmike@xxxxxxxxxx AIM: ncmikeday Yahoo: ultra.runner
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