From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760968AbZEGPb4 (ORCPT ); Thu, 7 May 2009 11:31:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755626AbZEGPbp (ORCPT ); Thu, 7 May 2009 11:31:45 -0400 Received: from mx2.redhat.com ([66.187.237.31]:40252 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754565AbZEGPbo (ORCPT ); Thu, 7 May 2009 11:31:44 -0400 Message-ID: <4A02FECC.6060609@redhat.com> Date: Thu, 07 May 2009 18:31:24 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Mark Langsdorf CC: Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: [PATCH][KVM][retry 1] Add support for Pause Filtering to AMD SVM References: <200905050909.58583.mark.langsdorf@amd.com> <20090507135522.GJ4059@amd.com> <200905071000.14038.mark.langsdorf@amd.com> In-Reply-To: <200905071000.14038.mark.langsdorf@amd.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (copying Ingo) Mark Langsdorf wrote: > commit 01813db8627e74018c8cec90df7e345839351f23 > Author: root > Date: Thu May 7 09:44:10 2009 -0500 > > New AMD processors will support the Pause Filter Feature. > This feature creates a new field in the VMCB called Pause > Filter Count. If Pause Filter Count is greater than 0 and > intercepting PAUSEs is enabled, the processor will increment > an internal counter when a PAUSE instruction occurs instead > of intercepting. When the internal counter reaches the > Pause Filter Count value, a PAUSE intercept will occur. > > This feature can be used to detect contended spinlocks, > especially when the lock holding VCPU is not scheduled. > Rescheduling another VCPU prevents the VCPU seeking the > lock from wasting its quantum by spinning idly. > > Experimental results show that most spinlocks are held > for less than 1000 PAUSE cycles or more than a few > thousand. Default the Pause Filter Counter to 3000 to > detect the contended spinlocks. > > Processor support for this feature is indicated by a CPUID > bit. > > On a 24 core system running 4 guests each with 16 VCPUs, > this patch improved overall performance of each guest's > 32 job kernbench by approximately 1%. Further performance > improvement may be possible with a more sophisticated > yield algorithm. > > -Mark Langsdorf > Operating System Research Center > AMD > > Signed-off-by: Mark Langsdorf > (please use git format-patch rather than git show, and set up user.name and user.email properly) > > svm->nested_vmcb = 0; > svm->vcpu.arch.hflags = HF_GIF_MASK; > + > + if (svm_has(SVM_FEATURE_PAUSE_FILTER)) { > + control->pause_filter_count = 5000; > + control->intercept |= (1ULL << INTERCEPT_PAUSE); > + } > + > } 3000 or 5000? > > +static int pause_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run) > +{ > + /* Simple yield */ > + vcpu_put(&svm->vcpu); > + schedule(); > + vcpu_load(&svm->vcpu); > + return 1; > + Ingo, will this do anything under CFS, or will CFS note that nothing has changed in the accounting and reschedule us immediately? -- error compiling committee.c: too many arguments to function