From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753050AbdF0NlU (ORCPT ); Tue, 27 Jun 2017 09:41:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58456 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752835AbdF0NlK (ORCPT ); Tue, 27 Jun 2017 09:41:10 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 3AC7B4E05D Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=rkrcmar@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 3AC7B4E05D Date: Tue, 27 Jun 2017 15:40:44 +0200 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Paolo Bonzini Cc: Wanpeng Li , 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 Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll Message-ID: <20170627134043.GA1487@potion> 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> <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 27 Jun 2017 13:41:00 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2017-06-27 14:28+0200, Paolo Bonzini: > 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. Right, it's just harder to use than host's single_task_running() -- the VCPU calling vcpu_is_preempted() is never preempted, so we have to look at other VCPUs that are not halted, but still preempted. If we see some ratio of preempted VCPUs (> 0?), then we stop polling and yield to the host. Working under the assumption that there is work for this PCPU if other VCPUs have stuff to do. The downside is that it misses information about host's topology, so it would be hard to make it work well. 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: =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= Message-Id: <20170627134043.GA1487@potion> Date: Tue, 27 Jun 2017 15:40:44 +0200 To: Paolo Bonzini Cc: Wanpeng Li , 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@ikuai8.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 List-ID: MjAxNy0wNi0yNyAxNDoyOCswMjAwLCBQYW9sbyBCb256aW5pOgo+IE9uIDI3LzA2LzIwMTcgMTQ6 MjMsIFdhbnBlbmcgTGkgd3JvdGU6Cj4+Pj4+IEkgaGF2ZSBjb25zaWRlcmVkIHNpbmdsZV90YXNr X3J1bm5pbmcoKSBiZWZvcmUuIEJ1dCBzaW5jZSB0aGVyZSBpcyBubwo+Pj4+PiBzdWNoIHBhcmF2 aXJ0dWFsIGludGVyZmFjZSBjdXJyZW50bHkgYW5kIGkgYW0gbm90IHN1cmUgd2hldGhlciBpdCBp cyBhCj4+Pj4+IGluZm9ybWF0aW9uIGxlYWsgZnJvbSBob3N0IGlmIGludHJvZHVjaW5nIHN1Y2gg aW50ZXJmYWNlLCBzbyBpIGRpZG4ndCBkbwo+Pj4+PiBpdC4gRG8geW91IG1lYW4gdmNwdV9pc19w cmVlbXB0ZWQgY2FuIGRvIHRoZSBzYW1lIHRoaW5nPyBJIGNoZWNrIHRoZQo+Pj4+PiBjb2RlIGFu ZCBzZWVtcyBpdCBvbmx5IHRlbGxzIHdoZXRoZXIgdGhlIFZDUFUgaXMgc2NoZWR1bGVkIG91dCBv ciBub3QKPj4+Pj4gd2hpY2ggY2Fubm90IHNhdGlzZnkgdGhlIG5lZWRzLgo+Pj4+IENhbiB5b3Ug aGVscCB0byBhbnN3ZXIgbXkgY29uZnVzaW9uPyBJIGhhdmUgZG91YmxlIGNoZWNrZWQgdGhlIGNv ZGUsIGJ1dAo+Pj4+IHN0aWxsIG5vdCBnZXQgeW91ciBwb2ludC4gRG8geW91IHRoaW5rIGl0IGlz IG5lY2Vzc2FyeSB0byBpbnRyb2R1Y2UgYW4KPj4+PiBwYXJhdmlydHVhbCBpbnRlcmZhY2UgdG8g ZXhwb3NlIHNpbmdsZV90YXNrX3J1bm5pbmcoKSB0byBndWVzdD8KPj4KPj4gSSB0aGluayB2Y3B1 X2lzX3ByZWVtcHRlZCBpcyBhIGdvb2QgZW5vdWdoIHJlcGxhY2VtZW50Lgo+PiBGb3IgZXhhbXBs ZSwgdmNwdS0+YXJjaC5zdC5zdGVhbC5wcmVlbXB0ZWQgaXMgMCB3aGVuIHRoZSB2Q1BVIGlzIHNj aGVkCj4+IGluIGFuZCB2bWVudHJ5LCB0aGVuIHNldmVyYWwgdGFza3MgYXJlIGVucXVldWVkIG9u IHRoZSBzYW1lIHBDUFUgYW5kCj4+IHdhaXRpbmcgb24gY2ZzIHJlZC1ibGFjayB0cmVlLCB0aGUg Z3Vlc3Qgc2hvdWxkIGF2b2lkIHRvIHBvbGwgaW4gdGhpcwo+PiBzY2VuYXJpbywgaG93ZXZlciwg dmNwdV9pc19wcmVlbXB0ZWQgcmV0dXJucyBmYWxzZSBhbmQgZ3Vlc3QgZGVjaWRlcwo+PiB0byBw b2xsLgo+IAo+IC4uLiB3aGljaCBpcyBub3QgbmVjZXNzYXJpbHkgX3dyb25nXy4gIEl0J3MganVz dCBhIGRpZmZlcmVudCBoZXVyaXN0aWMuCgpSaWdodCwgaXQncyBqdXN0IGhhcmRlciB0byB1c2Ug dGhhbiBob3N0J3Mgc2luZ2xlX3Rhc2tfcnVubmluZygpIC0tIHRoZQpWQ1BVIGNhbGxpbmcgdmNw dV9pc19wcmVlbXB0ZWQoKSBpcyBuZXZlciBwcmVlbXB0ZWQsIHNvIHdlIGhhdmUgdG8gbG9vawph dCBvdGhlciBWQ1BVcyB0aGF0IGFyZSBub3QgaGFsdGVkLCBidXQgc3RpbGwgcHJlZW1wdGVkLgoK SWYgd2Ugc2VlIHNvbWUgcmF0aW8gb2YgcHJlZW1wdGVkIFZDUFVzICg+IDA/KSwgdGhlbiB3ZSBz dG9wIHBvbGxpbmcgYW5kCnlpZWxkIHRvIHRoZSBob3N0LiAgV29ya2luZyB1bmRlciB0aGUgYXNz dW1wdGlvbiB0aGF0IHRoZXJlIGlzIHdvcmsgZm9yCnRoaXMgUENQVSBpZiBvdGhlciBWQ1BVcyBo YXZlIHN0dWZmIHRvIGRvLiAgVGhlIGRvd25zaWRlIGlzIHRoYXQgaXQKbWlzc2VzIGluZm9ybWF0 aW9uIGFib3V0IGhvc3QncyB0b3BvbG9neSwgc28gaXQgd291bGQgYmUgaGFyZCB0byBtYWtlIGl0 Cndvcmsgd2VsbC4KLS0tClRvIHVuc3Vic2NyaWJlIGZyb20gdGhpcyBsaXN0OiBzZW5kIHRoZSBs aW5lICJ1bnN1YnNjcmliZSBsaW51eC1lZGFjIiBpbgp0aGUgYm9keSBvZiBhIG1lc3NhZ2UgdG8g bWFqb3Jkb21vQHZnZXIua2VybmVsLm9yZwpNb3JlIG1ham9yZG9tbyBpbmZvIGF0ICBodHRwOi8v dmdlci5rZXJuZWwub3JnL21ham9yZG9tby1pbmZvLmh0bWwK From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll Date: Tue, 27 Jun 2017 15:40:44 +0200 Message-ID: <20170627134043.GA1487@potion> 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> <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Wanpeng Li , 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, To: Paolo Bonzini Return-path: Received: from mx1.redhat.com ([209.132.183.28]:58456 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752835AbdF0NlK (ORCPT ); Tue, 27 Jun 2017 09:41:10 -0400 Content-Disposition: inline In-Reply-To: <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 2017-06-27 14:28+0200, Paolo Bonzini: > 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. Right, it's just harder to use than host's single_task_running() -- the VCPU calling vcpu_is_preempted() is never preempted, so we have to look at other VCPUs that are not halted, but still preempted. If we see some ratio of preempted VCPUs (> 0?), then we stop polling and yield to the host. Working under the assumption that there is work for this PCPU if other VCPUs have stuff to do. The downside is that it misses information about host's topology, so it would be hard to make it work well.