Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752962AbdF0M2w (ORCPT ); Tue, 27 Jun 2017 08:28:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2901 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751524AbdF0M2n (ORCPT ); Tue, 27 Jun 2017 08:28:43 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 749728F226 Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=pbonzini@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 749728F226 Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll To: Wanpeng Li 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 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: Paolo Bonzini Message-ID: <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> Date: Tue, 27 Jun 2017 14:28:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 27 Jun 2017 12:28:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1265 Lines: 27 On 27/06/2017 14:23, Wanpeng Li wrote: >>>> 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. ... which is not necessarily _wrong_. It's just a different heuristic. In the end, the guest could run with "idle=poll" even, and there's little the host scheduler can do about it, except treating it as a CPU bound task. Paolo