From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3C57C282CE for ; Wed, 22 May 2019 15:08:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A331A20879 for ; Wed, 22 May 2019 15:08:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729752AbfEVPIL (ORCPT ); Wed, 22 May 2019 11:08:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:20651 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728466AbfEVPIL (ORCPT ); Wed, 22 May 2019 11:08:11 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EDCAD3087946; Wed, 22 May 2019 15:08:05 +0000 (UTC) Received: from amt.cnet (ovpn-112-15.gru2.redhat.com [10.97.112.15]) by smtp.corp.redhat.com (Postfix) with ESMTP id 665125D6A9; Wed, 22 May 2019 15:08:04 +0000 (UTC) Received: from amt.cnet (localhost [127.0.0.1]) by amt.cnet (Postfix) with ESMTP id 7FEDC10518F; Wed, 22 May 2019 12:07:42 -0300 (BRT) Received: (from marcelo@localhost) by amt.cnet (8.14.7/8.14.7/Submit) id x4MF7cfG003044; Wed, 22 May 2019 12:07:38 -0300 Date: Wed, 22 May 2019 12:07:38 -0300 From: Marcelo Tosatti To: Christian Borntraeger Cc: Paolo Bonzini , kvm-devel , Radim =?utf-8?B?S3LEjW3DocWZ?= , Andrea Arcangeli , "Rafael J. Wysocki" , Peter Zijlstra , Wanpeng Li , Konrad Rzeszutek Wilk , "Raslan, KarimAllah" , Boris Ostrovsky , Ankur Arora Subject: Re: [PATCH] x86: add cpuidle_kvm driver to allow guest side halt polling Message-ID: <20190522150735.GB2317@amt.cnet> References: <20190517174857.GA8611@amt.cnet> <352694a5-cc07-8fda-1dd2-2bf8be6e4dd2@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <352694a5-cc07-8fda-1dd2-2bf8be6e4dd2@de.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Wed, 22 May 2019 15:08:11 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, May 20, 2019 at 03:46:50PM +0200, Christian Borntraeger wrote: > > > On 20.05.19 14:07, Christian Borntraeger wrote: > > > > > > On 20.05.19 13:51, Paolo Bonzini wrote: > >> On 17/05/19 19:48, Marcelo Tosatti wrote: > >>> > >>> The cpuidle_kvm driver allows the guest vcpus to poll for a specified > >>> amount of time before halting. This provides the following benefits > >>> to host side polling: > >>> > >>> 1) The POLL flag is set while polling is performed, which allows > >>> a remote vCPU to avoid sending an IPI (and the associated > >>> cost of handling the IPI) when performing a wakeup. > >>> > >>> 2) The HLT VM-exit cost can be avoided. > >>> > >>> The downside of guest side polling is that polling is performed > >>> even with other runnable tasks in the host. > >>> > >>> Results comparing halt_poll_ns and server/client application > >>> where a small packet is ping-ponged: > >>> > >>> host --> 31.33 > >>> halt_poll_ns=300000 / no guest busy spin --> 33.40 (93.8%) > >>> halt_poll_ns=0 / guest_halt_poll_ns=300000 --> 32.73 (95.7%) > >>> > >>> For the SAP HANA benchmarks (where idle_spin is a parameter > >>> of the previous version of the patch, results should be the > >>> same): > >>> > >>> hpns == halt_poll_ns > >>> > >>> idle_spin=0/ idle_spin=800/ idle_spin=0/ > >>> hpns=200000 hpns=0 hpns=800000 > >>> DeleteC06T03 (100 thread) 1.76 1.71 (-3%) 1.78 (+1%) > >>> InsertC16T02 (100 thread) 2.14 2.07 (-3%) 2.18 (+1.8%) > >>> DeleteC00T01 (1 thread) 1.34 1.28 (-4.5%) 1.29 (-3.7%) > >>> UpdateC00T03 (1 thread) 4.72 4.18 (-12%) 4.53 (-5%) > >> > >> Hi Marcelo, > >> > >> some quick observations: > >> > >> 1) This is actually not KVM-specific, so the name and placement of the > >> docs should be adjusted. > >> > >> 2) Regarding KVM-specific code, however, we could add an MSR so that KVM > >> disables halt_poll_ns for this VM when this is active in the guest? > > > > The whole code looks pretty much architecture independent. I have also seen cases > > on s390 where this kind of code would make sense. Can we try to make this > > usable for other archs as well? > > I did a quick hack (not yet for the list as it contains some uglyness). > and the code seems to run ok on s390. > So any chance to move this into drivers/cpuidle/ so that !x86 can also enable that > when appropriate? Done that, but you have to provide default_idle function and then later change: +config HALTPOLL_CPUIDLE + tristate "Halt poll cpuidle driver" + depends on X86 + default y + help > I actually agree with Paolo that we should disable host halt polling as soon as > the guest does it. Maybe we should have some arch specific callback (that can be > an MSR). Yep.