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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 5840EECDE5F for ; Thu, 19 Jul 2018 13:35:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11F6B2084C for ; Thu, 19 Jul 2018 13:35:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 11F6B2084C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731829AbeGSOSM (ORCPT ); Thu, 19 Jul 2018 10:18:12 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:43282 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731126AbeGSOSM (ORCPT ); Thu, 19 Jul 2018 10:18:12 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A2F847A7E5; Thu, 19 Jul 2018 13:34:59 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-175.bos.redhat.com [10.18.17.175]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4FBFF111AF17; Thu, 19 Jul 2018 13:34:58 +0000 (UTC) Subject: Re: [PATCH] x86/kvm: Don't use pvqspinlock code if only 1 vCPU To: Konrad Rzeszutek Wilk Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Joe Mario References: <1531864767-30648-1-git-send-email-longman@redhat.com> <20180719011546.GB28585@char.US.ORACLE.com> From: Waiman Long Organization: Red Hat Message-ID: <24e1962a-075c-8168-5d95-033b826ee919@redhat.com> Date: Thu, 19 Jul 2018 09:34:58 -0400 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: <20180719011546.GB28585@char.US.ORACLE.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 19 Jul 2018 13:34:59 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 19 Jul 2018 13:34:59 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'longman@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/18/2018 09:15 PM, Konrad Rzeszutek Wilk wrote: > On Tue, Jul 17, 2018 at 05:59:27PM -0400, Waiman Long wrote: >> On a VM with only 1 vCPU, the locking fast path will always be >> successful. In this case, there is no need to use the the PV qspinlock >> code which has higher overhead on the unlock side than the native >> qspinlock code. > Why not make this global? That is for both KVM and Xen and any > other virtualized guest that uses this? Right, I will send another patch for Xen. The pvqspinlock code has to be explicitly opted in. Right now, both Xen and KVM used it in the tree. I am not sure about other out-of-tree modules. There is nothing I can do for those. Cheers, Longman