From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763954AbZEHSof (ORCPT ); Fri, 8 May 2009 14:44:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757648AbZEHSoY (ORCPT ); Fri, 8 May 2009 14:44:24 -0400 Received: from mx2.redhat.com ([66.187.237.31]:55950 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754281AbZEHSoX (ORCPT ); Fri, 8 May 2009 14:44:23 -0400 Message-ID: <4A047D86.1070407@redhat.com> Date: Fri, 08 May 2009 21:44:22 +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 Subject: Re: [PATCH][KVM][retry 2] 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> <200905081203.55484.mark.langsdorf@amd.com> In-Reply-To: <200905081203.55484.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 Mark Langsdorf wrote: > From 01813db8627e74018c8cec90df7e345839351f23 Mon Sep 17 00:00:00 2001 > From: Mark Langsdorf > Date: Thu, 7 May 2009 09:44:10 -0500 > Subject: [PATCH] Add support for Pause Filtering to AMD SVM > What's the differences wrt retry 1? > 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. > 3000. > 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. > Like I mentioned earlier, I don't think schedule() does anything on CFS. Try sched_yield(), but set /proc/sys/kernel/sched_compat_yield. > + > + if (svm_has(SVM_FEATURE_PAUSE_FILTER)) { > + control->pause_filter_count = 5000; > + control->intercept |= (1ULL << INTERCEPT_PAUSE); > + } > + > Here, 5000? > } > > static int svm_vcpu_reset(struct kvm_vcpu *vcpu) > @@ -2087,6 +2094,15 @@ static int interrupt_window_interception(struct vcpu_svm *svm, > return 1; > } > > +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; > +} > + > You don't need to vcpu_put() and vcpu_load(). The scheduler will call them for you if/when it switches tasks. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.