Re: VM performance issue in KVM guests.

From: Peter Zijlstra
Date: Fri Apr 16 2010 - 06:40:40 EST


On Thu, 2010-04-15 at 09:43 -0700, Srivatsa Vaddagiri wrote:
> On Thu, Apr 15, 2010 at 03:33:18PM +0200, Peter Zijlstra wrote:
> > On Thu, 2010-04-15 at 11:18 +0300, Avi Kivity wrote:
> > >
> > > Certainly that has even greater potential for Linux guests. Note that
> > > we spin on mutexes now, so we need to prevent preemption while the lock
> > > owner is running.
> >
> > either that, or disable spinning on (para) virt kernels. Para virt
> > kernels could possibly extend the thing by also checking to see if the
> > owner's vcpu is running.
>
> I suspect we will need a combination of both approaches, given that we will not
> be able to avoid preempting guests in their critical section always (too long
> critical sections or real-time tasks wanting to preempt). Other idea is to
> gang-schedule VCPUs of the same guest as much as possible?

Except gang scheduling is a scalability nightmare waiting to happen. I
much prefer this hint thing.
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