From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH] [RESEND] KVM:VMX: Add support for Pause-Loop Exiting Date: Sun, 27 Sep 2009 15:46:50 +0200 Message-ID: <20090927134650.GC29634@8bytes.org> References: <4ABA2AD7.6080008@intel.com> <4ABA2C22.7020000@redhat.com> <20090925204339.GA29634@8bytes.org> <4ABF22D9.3040308@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Zhai, Edwin" , Ingo Molnar , "kvm@vger.kernel.org" To: Avi Kivity Return-path: Received: from 8bytes.org ([88.198.83.132]:38697 "EHLO 8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752679AbZI0Nqs (ORCPT ); Sun, 27 Sep 2009 09:46:48 -0400 Content-Disposition: inline In-Reply-To: <4ABF22D9.3040308@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Sep 27, 2009 at 10:31:21AM +0200, Avi Kivity wrote: > On 09/25/2009 11:43 PM, Joerg Roedel wrote: >> On Wed, Sep 23, 2009 at 05:09:38PM +0300, Avi Kivity wrote: >> >>> We haven't sorted out what is the correct thing to do here. I think we >>> should go for a directed yield, but until we have it, you can use >>> hrtimers to sleep for 100 microseconds and hope the holding vcpu will >>> get scheduled. Even if it doesn't, we're only wasting a few percent cpu >>> time instead of spinning. >>> >> How do you plan to find out to which vcpu thread the current thread >> should yield? >> > > We can't find exactly which vcpu, but we can: > > - rule out threads that are not vcpus for this guest > - rule out threads that are already running > > A major problem with sleep() is that it effectively reduces the vm > priority relative to guests that don't have spinlock contention. By > selecting a random nonrunnable vcpu belonging to this guest, we at least > preserve the guest's timeslice. Ok, that makes sense. But before trying that we should probably try to call just yield() instead of schedule()? I remember someone from our team here at AMD did this for Xen a while ago and already had pretty good results with that. Xen has a completly other scheduler but maybe its worth trying? Joerg