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 16:07:53 +0200 Message-ID: <20090927140752.GD29634@8bytes.org> References: <4ABA2AD7.6080008@intel.com> <4ABA2C22.7020000@redhat.com> <20090925204339.GA29634@8bytes.org> <4ABF22D9.3040308@redhat.com> <20090927134650.GC29634@8bytes.org> <4ABF6D0B.8080603@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]:45718 "EHLO 8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752912AbZI0OHu (ORCPT ); Sun, 27 Sep 2009 10:07:50 -0400 Content-Disposition: inline In-Reply-To: <4ABF6D0B.8080603@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Sep 27, 2009 at 03:47:55PM +0200, Avi Kivity wrote: > On 09/27/2009 03:46 PM, Joerg Roedel wrote: >> >>> 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? >> > > yield() is a no-op in CFS. Hmm, true. At least when kernel.sched_compat_yield == 0, which it is on my distro. If the scheduler would give us something like a real_yield() function which asumes kernel.sched_compat_yield = 1 might help. At least its better than sleeping for some random amount of time. Joerg