Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752989AbdF0MXg (ORCPT ); Tue, 27 Jun 2017 08:23:36 -0400 Received: from mail-ot0-f195.google.com ([74.125.82.195]:33952 "EHLO mail-ot0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751612AbdF0MX2 (ORCPT ); Tue, 27 Jun 2017 08:23:28 -0400 MIME-Version: 1.0 In-Reply-To: References: <1498130534-26568-1-git-send-email-root@ip-172-31-39-62.us-west-2.compute.internal> <1498130534-26568-3-git-send-email-root@ip-172-31-39-62.us-west-2.compute.internal> <4444ffc8-9e7b-5bd2-20da-af422fe834cc@redhat.com> <2245bef7-b668-9265-f3f8-3b63d71b1033@gmail.com> <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> From: Wanpeng Li Date: Tue, 27 Jun 2017 20:23:27 +0800 Message-ID: Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll To: Paolo Bonzini Cc: Yang Zhang , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "the arch/x86 maintainers" , Jonathan Corbet , tony.luck@intel.com, Borislav Petkov , Peter Zijlstra , mchehab@kernel.org, Andrew Morton , krzk@kernel.org, jpoimboe@redhat.com, Andy Lutomirski , Christian Borntraeger , Thomas Garnier , Robert Gerst , Mathias Krause , douly.fnst@cn.fujitsu.com, Nicolai Stange , Frederic Weisbecker , dvlasenk@redhat.com, Daniel Bristot de Oliveira , yamada.masahiro@socionext.com, mika.westerberg@linux.intel.com, Chen Yu , aaron.lu@intel.com, Steven Rostedt , Kyle Huey , Len Brown , Prarit Bhargava , hidehiro.kawai.ez@hitachi.com, fengtiantian@huawei.com, pmladek@suse.com, jeyu@redhat.com, Larry.Finger@lwfinger.net, zijun_hu@htc.com, luisbg@osg.samsung.com, johannes.berg@intel.com, niklas.soderlund+renesas@ragnatech.se, zlpnobody@gmail.com, Alexey Dobriyan , fgao@48lvckh6395k16k5.yundunddos.com, ebiederm@xmission.com, Subash Abhinov Kasiviswanathan , Arnd Bergmann , Matt Fleming , Mel Gorman , "linux-kernel@vger.kernel.org" , linux-doc@vger.kernel.org, linux-edac@vger.kernel.org, kvm Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1434 Lines: 32 2017-06-27 20:07 GMT+08:00 Paolo Bonzini : > > > On 27/06/2017 13:22, Yang Zhang wrote: >>>> >>>> Regarding the good/bad idea part, KVM's polling is made much more >>>> acceptable by single_task_running(). At least you need to integrate it >>>> with paravirtualization. If the VM is scheduled out, you shrink the >>>> polling period. There is already vcpu_is_preempted for this, it is used >>>> by mutexes. >>> >>> I have considered single_task_running() before. But since there is no >>> such paravirtual interface currently and i am not sure whether it is a >>> information leak from host if introducing such interface, so i didn't do >>> it. Do you mean vcpu_is_preempted can do the same thing? I check the >>> code and seems it only tells whether the VCPU is scheduled out or not >>> which cannot satisfy the needs. >> >> Can you help to answer my confusion? I have double checked the code, but >> still not get your point. Do you think it is necessary to introduce an >> paravirtual interface to expose single_task_running() to guest? > > I think vcpu_is_preempted is a good enough replacement. For example, vcpu->arch.st.steal.preempted is 0 when the vCPU is sched in and vmentry, then several tasks are enqueued on the same pCPU and waiting on cfs red-black tree, the guest should avoid to poll in this scenario, however, vcpu_is_preempted returns false and guest decides to poll. Regards, Wanpeng Li