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Date: Wed, 1 Dec 2010 09:46:56 -0800
From: Chris Wright <chrisw@sous-sol.org>
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Subject: [Qemu-devel] Re: [PATCH] qemu-kvm: response to SIGUSR1 to
	start/stop a VCPU (v2)
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: kvm@vger.kernel.org, Mike Galbraith <efault@gmx.de>, qemu-devel@nongnu.org, vatsa@linux.vnet.ibm.com, Chris Wright <chrisw@sous-sol.org>, Anthony Liguori <aliguori@linux.vnet.ibm.com>, Avi Kivity <avi@redhat.com>

* Peter Zijlstra (a.p.zijlstra@chello.nl) wrote:
> On Wed, 2010-12-01 at 09:17 -0800, Chris Wright wrote:
> > Directed yield and fairness don't mix well either. You can end up
> > feeding the other tasks more time than you'll ever get back.
> 
> If the directed yield is always to another task in your cgroup then
> inter-guest scheduling fairness should be maintained. 
> 
> Yes, but not the inter-vcpu fairness.

That same vcpu doesn't get fair scheduling if it spends its entire
timeslice spinning on a lock held by a de-scheduled vcpu.