From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753808Ab2GKJHM (ORCPT ); Wed, 11 Jul 2012 05:07:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46893 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751717Ab2GKJHK (ORCPT ); Wed, 11 Jul 2012 05:07:10 -0400 Message-ID: <4FFD422B.9060008@redhat.com> Date: Wed, 11 Jul 2012 12:06:51 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 MIME-Version: 1.0 To: Christian Borntraeger CC: Raghavendra K T , "H. Peter Anvin" , Thomas Gleixner , Marcelo Tosatti , Ingo Molnar , Rik van Riel , S390 , Carsten Otte , KVM , chegu vinod , "Andrew M. Theurer" , LKML , X86 , Gleb Natapov , linux390@de.ibm.com, Srivatsa Vaddagiri , Joerg Roedel Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler References: <20120709062012.24030.37154.sendpatchset@codeblue> <4FFA8E5E.3070108@de.ibm.com> In-Reply-To: <4FFA8E5E.3070108@de.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/09/2012 10:55 AM, Christian Borntraeger wrote: > On 09/07/12 08:20, Raghavendra K T wrote: >> Currently Pause Looop Exit (PLE) handler is doing directed yield to a >> random VCPU on PL exit. Though we already have filtering while choosing >> the candidate to yield_to, we can do better. >> >> Problem is, for large vcpu guests, we have more probability of yielding >> to a bad vcpu. We are not able to prevent directed yield to same guy who >> has done PL exit recently, who perhaps spins again and wastes CPU. >> >> Fix that by keeping track of who has done PL exit. So The Algorithm in series >> give chance to a VCPU which has: > > > We could do the same for s390. The appropriate exit would be diag44 (yield to hypervisor). > > Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though. Perhaps x86 should copy this. > So there is no win here, but there are other cases were diag44 is used, e.g. cpu_relax. > I have to double check with others, if these cases are critical, but for now, it seems > that your dummy implementation for s390 is just fine. After all it is a no-op until > we implement something. Does the data structure make sense for you? If so we can move it to common code (and manage it in kvm_vcpu_on_spin()). We can guard it with CONFIG_KVM_HAVE_CPU_RELAX_INTERCEPT or something, so other archs don't have to pay anything. -- error compiling committee.c: too many arguments to function