From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752759AbdF0LXX (ORCPT ); Tue, 27 Jun 2017 07:23:23 -0400 Received: from mail-ot0-f196.google.com ([74.125.82.196]:34052 "EHLO mail-ot0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751699AbdF0LXO (ORCPT ); Tue, 27 Jun 2017 07:23:14 -0400 Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll To: Paolo Bonzini , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com 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> 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 From: Yang Zhang Message-ID: <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> Date: Tue, 27 Jun 2017 19:22:57 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <2245bef7-b668-9265-f3f8-3b63d71b1033@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/6/23 11:58, Yang Zhang wrote: > On 2017/6/22 19:51, Paolo Bonzini wrote: >> >> >> On 22/06/2017 13:22, root wrote: >>> ============================================================== >>> >>> +poll_grow: (X86 only) >>> + >>> +This parameter is multiplied in the grow_poll_ns() to increase the >>> poll time. >>> +By default, the values is 2. >>> + >>> +============================================================== >>> +poll_shrink: (X86 only) >>> + >>> +This parameter is divided in the shrink_poll_ns() to reduce the poll >>> time. >>> +By default, the values is 2. >> >> Even before starting the debate on whether this is a good idea or a bad >> idea, KVM reduces the polling value to the minimum (10 us) by default > > I noticed it. It looks like the logic inside KVM is more reasonable. I > will do more testing to compare the two. > >> when polling fails. Also, it shouldn't be bound to >> CONFIG_HYPERVISOR_GUEST, since there's nothing specific to virtual >> machines here. > > Yes. The original idea to use CONFIG_HYPERVISOR_GUEST because this > mechanism will only helpful inside VM. But as Thomas mentioned on other > thread it is wrong to use it since most distribution kernel will set it > to yes and still affect the bare metal. I will integrate it with > paravirtualizaion part as you suggested in below. > >> >> 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. Hi Paolo 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? -- Yang Alibaba Cloud Computing From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: [2/2] x86/idle: use dynamic halt poll From: Yang Zhang Message-Id: <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> Date: Tue, 27 Jun 2017 19:22:57 +0800 To: Paolo Bonzini , 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@ikuai8.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 List-ID: T24gMjAxNy82LzIzIDExOjU4LCBZYW5nIFpoYW5nIHdyb3RlOgo+IE9uIDIwMTcvNi8yMiAxOTo1 MSwgUGFvbG8gQm9uemluaSB3cm90ZToKPj4KPj4KPj4gT24gMjIvMDYvMjAxNyAxMzoyMiwgcm9v dCB3cm90ZToKPj4+ICA9PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09 PT09PT09PT09PT09PT09PT09PQo+Pj4KPj4+ICtwb2xsX2dyb3c6IChYODYgb25seSkKPj4+ICsK Pj4+ICtUaGlzIHBhcmFtZXRlciBpcyBtdWx0aXBsaWVkIGluIHRoZSBncm93X3BvbGxfbnMoKSB0 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<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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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 To: Paolo Bonzini , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com Return-path: In-Reply-To: <2245bef7-b668-9265-f3f8-3b63d71b1033@gmail.com> Sender: linux-doc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 2017/6/23 11:58, Yang Zhang wrote: > On 2017/6/22 19:51, Paolo Bonzini wrote: >> >> >> On 22/06/2017 13:22, root wrote: >>> ============================================================== >>> >>> +poll_grow: (X86 only) >>> + >>> +This parameter is multiplied in the grow_poll_ns() to increase the >>> poll time. >>> +By default, the values is 2. >>> + >>> +============================================================== >>> +poll_shrink: (X86 only) >>> + >>> +This parameter is divided in the shrink_poll_ns() to reduce the poll >>> time. >>> +By default, the values is 2. >> >> Even before starting the debate on whether this is a good idea or a bad >> idea, KVM reduces the polling value to the minimum (10 us) by default > > I noticed it. It looks like the logic inside KVM is more reasonable. I > will do more testing to compare the two. > >> when polling fails. Also, it shouldn't be bound to >> CONFIG_HYPERVISOR_GUEST, since there's nothing specific to virtual >> machines here. > > Yes. The original idea to use CONFIG_HYPERVISOR_GUEST because this > mechanism will only helpful inside VM. But as Thomas mentioned on other > thread it is wrong to use it since most distribution kernel will set it > to yes and still affect the bare metal. I will integrate it with > paravirtualizaion part as you suggested in below. > >> >> 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. Hi Paolo 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? -- Yang Alibaba Cloud Computing