From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH v7 04/11] KVM: MMU: zap pages in batch Date: Mon, 27 May 2013 21:18:02 -0300 Message-ID: <20130528001802.GB1359@amt.cnet> References: <1369252560-11611-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <1369252560-11611-5-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <20130524203432.GB4525@amt.cnet> <51A2C2DC.6080403@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: gleb@redhat.com, avi.kivity@gmail.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org To: Xiao Guangrong Return-path: Content-Disposition: inline In-Reply-To: <51A2C2DC.6080403@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, May 27, 2013 at 10:20:12AM +0800, Xiao Guangrong wrote: > On 05/25/2013 04:34 AM, Marcelo Tosatti wrote: > > On Thu, May 23, 2013 at 03:55:53AM +0800, Xiao Guangrong wrote: > >> Zap at lease 10 pages before releasing mmu-lock to reduce the overload > >> caused by requiring lock > >> > >> After the patch, kvm_zap_obsolete_pages can forward progress anyway, > >> so update the comments > >> > >> [ It improves kernel building 0.6% ~ 1% ] > > > > Can you please describe the overload in more detail? Under what scenario > > is kernel building improved? > > Yes. > > The scenario is we do kernel building, meanwhile, repeatedly read PCI rom > every one second. > > [ > echo 1 > /sys/bus/pci/devices/0000\:00\:03.0/rom > cat /sys/bus/pci/devices/0000\:00\:03.0/rom > /dev/null > ] Can't see why it reflects real world scenario (or a real world scenario with same characteristics regarding kvm_mmu_zap_all vs faults)? Point is, it would be good to understand why this change is improving performance? What are these cases where breaking out of kvm_mmu_zap_all due to either (need_resched || spin_needbreak) on zapped < 10 ?