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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 AE13EC3A5A1 for ; Wed, 28 Aug 2019 14:49:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90E4A22CED for ; Wed, 28 Aug 2019 14:49:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726591AbfH1OtS (ORCPT ); Wed, 28 Aug 2019 10:49:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51982 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726867AbfH1OtR (ORCPT ); Wed, 28 Aug 2019 10:49:17 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6E6A02A09A7; Wed, 28 Aug 2019 14:49:17 +0000 (UTC) Received: from amt.cnet (ovpn-112-8.gru2.redhat.com [10.97.112.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 73B811001B00; Wed, 28 Aug 2019 14:49:14 +0000 (UTC) Received: from amt.cnet (localhost [127.0.0.1]) by amt.cnet (Postfix) with ESMTP id 2ED72105139; Wed, 28 Aug 2019 11:49:00 -0300 (BRT) Received: (from marcelo@localhost) by amt.cnet (8.14.7/8.14.7/Submit) id x7SEmxv8014289; Wed, 28 Aug 2019 11:48:59 -0300 Date: Wed, 28 Aug 2019 11:48:58 -0300 From: Marcelo Tosatti To: Wanpeng Li Cc: Paolo Bonzini , "Rafael J. Wysocki" , LKML , kvm , Radim =?utf-8?B?S3LEjW3DocWZ?= , Linux PM , "Michael S. Tsirkin" Subject: Re: [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available Message-ID: <20190828144858.GA14215@amt.cnet> References: <1564643196-7797-1-git-send-email-wanpengli@tencent.com> <7b1e3025-f513-7068-32ac-4830d67b65ac@intel.com> <20190803202058.GA9316@amt.cnet> <20190826204045.GA24697@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 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Wed, 28 Aug 2019 14:49:17 +0000 (UTC) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Tue, Aug 27, 2019 at 08:43:13AM +0800, Wanpeng Li wrote: > > > kvm adaptive halt-polling will compete with > > > vhost-kthreads, however, poll in guest unaware other runnable tasks in > > > the host which will defeat vhost-kthreads. > > > > It depends on how much work vhost-kthreads needs to do, how successful > > halt-poll in the guest is, and what improvement halt-polling brings. > > The amount of polling will be reduced to zero if polling > > is not successful. > > We observe vhost-kthreads compete with vCPUs adaptive halt-polling in > kvm, it hurt performance in over-subscribe product environment, > polling in guest can make it worse. > > Regards, > Wanpeng Li Wanpeng, Polling should not be performed if there is other work to do. For example, halt-polling could check a host/guest shared memory region indicating whether there are other runnable tasks in the host. Disabling polling means you will not achieve the improvement even in the transitional periods where the system is not overcommitted (which should be frequent given that idling is common). Again, about your patch: it brings no benefit to anyone. Guest halt polling should be already disabled by default (the driver has to be loaded for guest polling to take place).