From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752986AbdF0MId (ORCPT ); Tue, 27 Jun 2017 08:08:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53602 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751524AbdF0MI0 (ORCPT ); Tue, 27 Jun 2017 08:08:26 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 05F73624B1 Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=pbonzini@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 05F73624B1 Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll To: Yang Zhang , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com Cc: x86@kernel.org, corbet@lwn.net, tony.luck@intel.com, bp@alien8.de, peterz@infradead.org, mchehab@kernel.org, akpm@linux-foundation.org, krzk@kernel.org, jpoimboe@redhat.com, luto@kernel.org, borntraeger@de.ibm.com, thgarnie@google.com, rgerst@gmail.com, minipli@googlemail.com, douly.fnst@cn.fujitsu.com, nicstange@gmail.com, fweisbec@gmail.com, dvlasenk@redhat.com, bristot@redhat.com, yamada.masahiro@socionext.com, mika.westerberg@linux.intel.com, yu.c.chen@intel.com, aaron.lu@intel.com, rostedt@goodmis.org, me@kylehuey.com, len.brown@intel.com, prarit@redhat.com, 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, adobriyan@gmail.com, fgao@48lvckh6395k16k5.yundunddos.com, ebiederm@xmission.com, subashab@codeaurora.org, arnd@arndb.de, matt@codeblueprint.co.uk, mgorman@techsingularity.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-edac@vger.kernel.org, kvm@vger.kernel.org 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: Date: Tue, 27 Jun 2017 14:07:56 +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: <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> 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 [10.5.110.39]); Tue, 27 Jun 2017 12:08:25 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Paolo