From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755160Ab1F2LOp (ORCPT ); Wed, 29 Jun 2011 07:14:45 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:62717 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753322Ab1F2LOo (ORCPT ); Wed, 29 Jun 2011 07:14:44 -0400 Message-ID: <4E0B0997.4090206@cn.fujitsu.com> Date: Wed, 29 Jun 2011 19:16:39 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 MIME-Version: 1.0 To: Avi Kivity CC: Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table References: <4E01FBC9.3020009@cn.fujitsu.com> <4E01FDB4.60306@cn.fujitsu.com> <4E0AED86.2060908@redhat.com> In-Reply-To: <4E0AED86.2060908@redhat.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-06-29 19:14:09, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-06-29 19:14:10, Serialize complete at 2011-06-29 19:14:10 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/29/2011 05:16 PM, Avi Kivity wrote: > On 06/22/2011 05:35 PM, Xiao Guangrong wrote: >> Use rcu to protect shadow pages table to be freed, so we can safely walk it, >> it should run fastly and is needed by mmio page fault >> > >> static void kvm_mmu_commit_zap_page(struct kvm *kvm, >> struct list_head *invalid_list) >> { >> @@ -1767,6 +1874,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm, >> >> kvm_flush_remote_tlbs(kvm); >> >> + if (atomic_read(&kvm->arch.reader_counter)) { >> + kvm_mmu_isolate_pages(invalid_list); >> + sp = list_first_entry(invalid_list, struct kvm_mmu_page, link); >> + list_del_init(invalid_list); >> + call_rcu(&sp->rcu, free_pages_rcu); >> + return; >> + } >> + > > I think we should do this unconditionally. The cost of ping-ponging the shared cache line containing reader_counter will increase with large smp counts. On the other hand, zap_page is very rare, so it can be a little slower. Also, less code paths = easier to understand. > On soft mmu, zap_page is very frequently, it can cause performance regression in my test.