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 DB2A0C6778A for ; Thu, 5 Jul 2018 12:41:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BCCF240C7 for ; Thu, 5 Jul 2018 12:41:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9BCCF240C7 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 S1754094AbeGEMlb (ORCPT ); Thu, 5 Jul 2018 08:41:31 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:48602 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753718AbeGEMl3 (ORCPT ); Thu, 5 Jul 2018 08:41:29 -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 84FB68577C; Thu, 5 Jul 2018 12:41:28 +0000 (UTC) Received: from [10.36.117.13] (ovpn-117-13.ams2.redhat.com [10.36.117.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 64BC1111E417; Thu, 5 Jul 2018 12:41:27 +0000 (UTC) Subject: Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly) To: "Raslan, KarimAllah" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" Cc: "rkrcmar@redhat.com" References: <1523744804-8220-1-git-send-email-karahmed@amazon.de> <53700469-74f0-f3b0-96a4-d8ace2919b36@redhat.com> <1527003728.13207.55.camel@amazon.de> <5f346c4e-73f2-6a73-7915-e9fa911191ec@redhat.com> <1530793361.23804.13.camel@amazon.de> From: Paolo Bonzini Openpgp: preference=signencrypt Autocrypt: addr=pbonzini@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <1530793361.23804.13.camel@amazon.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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, 05 Jul 2018 12:41:28 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 05 Jul 2018 12:41:28 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'pbonzini@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/07/2018 14:22, Raslan, KarimAllah wrote: >> They don't support atomics on double-word data. > But they support atomics on single words. Of which there are two. > We don't need atomic updates of the whole 64-bit quantity (a là  > cmpxchg). Do we strictly need this to be atomic accross the 64-bit? > > Looking at the use cases for "requests": > > kvm_clear_request > kvm_test_request > kvm_request_pending > kvm_check_request > > ... and all of them would still work if the atomicity is only at the  > word level, right? > Good point! Then yes, requests can be made 64 bit wide. Paolo