Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751860AbdHAIcl (ORCPT ); Tue, 1 Aug 2017 04:32:41 -0400 Received: from mail-wr0-f196.google.com ([209.85.128.196]:36684 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751805AbdHAIcg (ORCPT ); Tue, 1 Aug 2017 04:32:36 -0400 Subject: Re: [RFC] KVM: optimize the kvm_vcpu_on_spin To: "Longpeng (Mike)" Cc: David Hildenbrand , rkrcmar@redhat.com, agraf@suse.com, borntraeger@de.ibm.com, cohuck@redhat.com, christoffer.dall@linaro.org, marc.zyngier@arm.com, james.hogan@imgtec.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, weidong.huang@huawei.com, arei.gonglei@huawei.com, wangxinxin.wang@huawei.com, longpeng.mike@gmail.com References: <1501309377-195256-1-git-send-email-longpeng2@huawei.com> <597F1DAE.4020809@huawei.com> <0677ed6e-280a-d2f3-d873-1daf99b39551@redhat.com> <3572e95a-a5eb-748b-25c8-b7e128cbbe1b@redhat.com> <597FF4CE.7050901@huawei.com> From: Paolo Bonzini Message-ID: Date: Tue, 1 Aug 2017 10:32:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <597FF4CE.7050901@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1213 Lines: 35 On 01/08/2017 05:26, Longpeng (Mike) wrote: > > > On 2017/7/31 21:20, Paolo Bonzini wrote: > >> On 31/07/2017 14:27, David Hildenbrand wrote: >>>> I'm not sure whether the operation of get the vcpu's priority-level is >>>> expensive on all architectures, so I record it in kvm_sched_out() for >>>> minimal the extra cycles cost in kvm_vcpu_on_spin(). >>>> >>> as you only care for x86 right now either way, you can directly optimize >>> here for the good (here: x86) case (keeping changes and therefore >>> possible bugs minimal). >> >> I agree with Cornelia that this is inconsistent, so you shouldn't update >> me->in_kernmode in kvm_vcpu_on_spin. However, get_cpl requires >> vcpu_load on Intel x86, so Mike's patch is necessary (vmx_get_cpl -> >> vmx_read_guest_seg_ar -> vmcs_read32). >> > > Hi Paolo, > > It seems that other architectures(e.g. arm/s390) needn't to cache the result, > but x86 need, so I need to move 'in_kernmode' into kvm_vcpu_arch and only add > this field to x86, right? That's another way to do it, and I like it. >> This will cache the result until the next sched_in, so that > > 'until the next sched_in' --> Do we need to clear the result in sched in ? No, thanks. Paolo