From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751579AbdF0N5G (ORCPT ); Tue, 27 Jun 2017 09:57:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44796 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751466AbdF0N45 (ORCPT ); Tue, 27 Jun 2017 09:56:57 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 204CBC05FFDE Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=pbonzini@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 204CBC05FFDE Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= 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 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> <20170627134043.GA1487@potion> From: Paolo Bonzini Message-ID: <2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.com> Date: Tue, 27 Jun 2017 15:56:35 +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: <20170627134043.GA1487@potion> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 27 Jun 2017 13:56:57 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27/06/2017 15:40, Radim Krčmář wrote: >> ... 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. I would just use vcpu_is_preempted on the current CPU. From guest POV this option is really a "f*** everyone else" setting just like idle=poll, only a little more polite. If we've been preempted and we were polling, there are two cases. If an interrupt was queued while the guest was preempted, the poll will be treated as successful anyway. If it hasn't, let others run---but really that's not because the guest wants to be polite, it's to avoid that the scheduler penalizes it excessively. So until it's preempted, I think it's okay if the guest doesn't care about others. You wouldn't use this option anyway in overcommitted situations. (I'm still not very convinced about the idea). Paolo 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: Paolo Bonzini Message-Id: <2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.com> Date: Tue, 27 Jun 2017 15:56:35 +0200 To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= 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: T24gMjcvMDYvMjAxNyAxNTo0MCwgUmFkaW0gS3LEjW3DocWZIHdyb3RlOgo+PiAuLi4gd2hpY2gg aXMgbm90IG5lY2Vzc2FyaWx5IF93cm9uZ18uICBJdCdzIGp1c3QgYSBkaWZmZXJlbnQgaGV1cmlz dGljLgo+IFJpZ2h0LCBpdCdzIGp1c3QgaGFyZGVyIHRvIHVzZSB0aGFuIGhvc3QncyBzaW5nbGVf dGFza19ydW5uaW5nKCkgLS0gdGhlCj4gVkNQVSBjYWxsaW5nIHZjcHVfaXNfcHJlZW1wdGVkKCkg aXMgbmV2ZXIgcHJlZW1wdGVkLCBzbyB3ZSBoYXZlIHRvIGxvb2sKPiBhdCBvdGhlciBWQ1BVcyB0 aGF0IGFyZSBub3QgaGFsdGVkLCBidXQgc3RpbGwgcHJlZW1wdGVkLgo+IAo+IElmIHdlIHNlZSBz b21lIHJhdGlvIG9mIHByZWVtcHRlZCBWQ1BVcyAoPiAwPyksIHRoZW4gd2Ugc3RvcCBwb2xsaW5n IGFuZAo+IHlpZWxkIHRvIHRoZSBob3N0LiAgV29ya2luZyB1bmRlciB0aGUgYXNzdW1wdGlvbiB0 aGF0IHRoZXJlIGlzIHdvcmsgZm9yCj4gdGhpcyBQQ1BVIGlmIG90aGVyIFZDUFVzIGhhdmUgc3R1 ZmYgdG8gZG8uICBUaGUgZG93bnNpZGUgaXMgdGhhdCBpdAo+IG1pc3NlcyBpbmZvcm1hdGlvbiBh Ym91dCBob3N0J3MgdG9wb2xvZ3ksIHNvIGl0IHdvdWxkIGJlIGhhcmQgdG8gbWFrZSBpdAo+IHdv cmsgd2VsbC4KCkkgd291bGQganVzdCB1c2UgdmNwdV9pc19wcmVlbXB0ZWQgb24gdGhlIGN1cnJl bnQgQ1BVLiAgRnJvbSBndWVzdCBQT1YKdGhpcyBvcHRpb24gaXMgcmVhbGx5IGEgImYqKiogZXZl cnlvbmUgZWxzZSIgc2V0dGluZyBqdXN0IGxpa2UKaWRsZT1wb2xsLCBvbmx5IGEgbGl0dGxlIG1v cmUgcG9saXRlLgoKSWYgd2UndmUgYmVlbiBwcmVlbXB0ZWQgYW5kIHdlIHdlcmUgcG9sbGluZywg dGhlcmUgYXJlIHR3byBjYXNlcy4gIElmIGFuCmludGVycnVwdCB3YXMgcXVldWVkIHdoaWxlIHRo ZSBndWVzdCB3YXMgcHJlZW1wdGVkLCB0aGUgcG9sbCB3aWxsIGJlCnRyZWF0ZWQgYXMgc3VjY2Vz c2Z1bCBhbnl3YXkuICBJZiBpdCBoYXNuJ3QsIGxldCBvdGhlcnMgcnVuLS0tYnV0IHJlYWxseQp0 aGF0J3Mgbm90IGJlY2F1c2UgdGhlIGd1ZXN0IHdhbnRzIHRvIGJlIHBvbGl0ZSwgaXQncyB0byBh dm9pZCB0aGF0IHRoZQpzY2hlZHVsZXIgcGVuYWxpemVzIGl0IGV4Y2Vzc2l2ZWx5LgoKU28gdW50 aWwgaXQncyBwcmVlbXB0ZWQsIEkgdGhpbmsgaXQncyBva2F5IGlmIHRoZSBndWVzdCBkb2Vzbid0 IGNhcmUKYWJvdXQgb3RoZXJzLiAgWW91IHdvdWxkbid0IHVzZSB0aGlzIG9wdGlvbiBhbnl3YXkg aW4gb3ZlcmNvbW1pdHRlZApzaXR1YXRpb25zLgoKKEknbSBzdGlsbCBub3QgdmVyeSBjb252aW5j ZWQgYWJvdXQgdGhlIGlkZWEpLgoKUGFvbG8KLS0tClRvIHVuc3Vic2NyaWJlIGZyb20gdGhpcyBs aXN0OiBzZW5kIHRoZSBsaW5lICJ1bnN1YnNjcmliZSBsaW51eC1lZGFjIiBpbgp0aGUgYm9keSBv ZiBhIG1lc3NhZ2UgdG8gbWFqb3Jkb21vQHZnZXIua2VybmVsLm9yZwpNb3JlIG1ham9yZG9tbyBp bmZvIGF0ICBodHRwOi8vdmdlci5rZXJuZWwub3JnL21ham9yZG9tby1pbmZvLmh0bWwK From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll Date: Tue, 27 Jun 2017 15:56:35 +0200 Message-ID: <2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.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> <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> <20170627134043.GA1487@potion> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit 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: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Return-path: In-Reply-To: <20170627134043.GA1487@potion> Content-Language: en-US Sender: linux-doc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 27/06/2017 15:40, Radim Krčmář wrote: >> ... 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. I would just use vcpu_is_preempted on the current CPU. From guest POV this option is really a "f*** everyone else" setting just like idle=poll, only a little more polite. If we've been preempted and we were polling, there are two cases. If an interrupt was queued while the guest was preempted, the poll will be treated as successful anyway. If it hasn't, let others run---but really that's not because the guest wants to be polite, it's to avoid that the scheduler penalizes it excessively. So until it's preempted, I think it's okay if the guest doesn't care about others. You wouldn't use this option anyway in overcommitted situations. (I'm still not very convinced about the idea). Paolo