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[Xen-devel] Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support p

To: vatsa@xxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock
From: Rik van Riel <riel@xxxxxxxxxx>
Date: Fri, 21 Jan 2011 09:48:29 -0500
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Américo , Nick Piggin <npiggin@xxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, suzuki@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, Wang <xiyou.wangcong@xxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
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On 01/21/2011 09:02 AM, Srivatsa Vaddagiri wrote:
On Thu, Jan 20, 2011 at 09:56:27AM -0800, Jeremy Fitzhardinge wrote:
  The key here is not to
sleep when waiting for locks (as implemented by current patch-series, which can
put other VMs at an advantage by giving them more time than they are entitled

Why?  If a VCPU can't make progress because its waiting for some
resource, then why not schedule something else instead?

In the process, "something else" can get more share of cpu resource than its
entitled to and that's where I was bit concerned. I guess one could
employ hard-limits to cap "something else's" bandwidth where it is of real
concern (like clouds).

I'd like to think I fixed those things in my yield_task_fair +
yield_to + kvm_vcpu_on_spin patch series from yesterday.


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