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 0186FC04AAC for ; Mon, 20 May 2019 15:23:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4FDB2054F for ; Mon, 20 May 2019 15:23:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388127AbfETPXh (ORCPT ); Mon, 20 May 2019 11:23:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60632 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731389AbfETPXh (ORCPT ); Mon, 20 May 2019 11:23:37 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4C1EBC02938A; Mon, 20 May 2019 15:23:32 +0000 (UTC) Received: from amt.cnet (ovpn-112-3.gru2.redhat.com [10.97.112.3]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2636061D13; Mon, 20 May 2019 15:23:27 +0000 (UTC) Received: from amt.cnet (localhost [127.0.0.1]) by amt.cnet (Postfix) with ESMTP id 1361F10518C; Mon, 20 May 2019 09:49:48 -0300 (BRT) Received: (from marcelo@localhost) by amt.cnet (8.14.7/8.14.7/Submit) id x4KCnihw003938; Mon, 20 May 2019 09:49:44 -0300 Date: Mon, 20 May 2019 09:49:44 -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: <20190520124940.GB3800@amt.cnet> References: <20190517174857.GA8611@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 20 May 2019 15:23:37 +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 02:07:09PM +0200, 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? Will move to drivers/cpuidle/