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 E1594C04AB5 for ; Thu, 6 Jun 2019 18:36:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BB4BC20872 for ; Thu, 6 Jun 2019 18:36:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727939AbfFFSgp (ORCPT ); Thu, 6 Jun 2019 14:36:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54870 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726719AbfFFSgp (ORCPT ); Thu, 6 Jun 2019 14:36:45 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E2AAA3079B63; Thu, 6 Jun 2019 18:36:40 +0000 (UTC) Received: from ultra.random (ovpn-120-155.rdu2.redhat.com [10.10.120.155]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4DF335C2E6; Thu, 6 Jun 2019 18:36:33 +0000 (UTC) Date: Thu, 6 Jun 2019 14:36:32 -0400 From: Andrea Arcangeli To: Joao Martins Cc: Marcelo Tosatti , kvm-devel , Paolo Bonzini , Radim Krcmar , "Rafael J. Wysocki" , Peter Zijlstra , Wanpeng Li , Konrad Rzeszutek Wilk , Raslan KarimAllah , Boris Ostrovsky , Ankur Arora , Christian Borntraeger Subject: Re: [patch v2 3/3] cpuidle-haltpoll: disable host side polling when kvm virtualized Message-ID: <20190606183632.GA20928@redhat.com> References: <20190603225242.289109849@amt.cnet> <20190603225254.360289262@amt.cnet> <20190604122404.GA18979@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Thu, 06 Jun 2019 18:36:45 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hello, On Thu, Jun 06, 2019 at 07:25:28PM +0100, Joao Martins wrote: > But I wonder whether we should fail to load cpuidle-haltpoll when host halt > polling can't be disabled[*]? That is to avoid polling in both host and guest > and *possibly* avoid chances for performance regressions when running on older > hypervisors? I don't think it's necessary: that would force an upgrade of the host KVM version in order to use the guest haltpoll feature with an upgraded guest kernel that can use the guest haltpoll. The guest haltpoll is self contained in the guest, so there's no reason to prevent that by design or to force upgrade of the KVM host version. It'd be more than enough to reload kvm.ko in the host with the host haltpoll set to zero with the module parameter already available, to achieve the same runtime without requiring a forced host upgrade. The warning however sounds sensible. Thanks, Andrea