From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 3D693201; Mon, 27 Nov 2017 09:27:31 +0100 (CET) Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5FF185D5E6; Mon, 27 Nov 2017 08:27:31 +0000 (UTC) Received: from [10.36.112.50] (ovpn-112-50.ams2.redhat.com [10.36.112.50]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6584660603; Mon, 27 Nov 2017 08:27:25 +0000 (UTC) To: Victor Kaplansky Cc: dev@dpdk.org, yliu@fridaylinux.org, tiwei bie , jianfeng tan , stable@dpdk.org, jfreiman@redhat.com References: <20171124180826.18439-1-maxime.coquelin@redhat.com> <20171124180826.18439-3-maxime.coquelin@redhat.com> <1760091245.45753170.1511770580954.JavaMail.zimbra@redhat.com> From: Maxime Coquelin Message-ID: <0a577e7b-2d90-04ba-3fac-f70192970a09@redhat.com> Date: Mon, 27 Nov 2017 09:27:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1760091245.45753170.1511770580954.JavaMail.zimbra@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 27 Nov 2017 08:27:31 +0000 (UTC) Subject: Re: [dpdk-dev] [PATCH v2 2/3] vhost: protect dirty logging against logging base change X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 27 Nov 2017 08:27:32 -0000 Hi Victor, On 11/27/2017 09:16 AM, Victor Kaplansky wrote: > Hi, > > While I agree that taking full fledged lock by rte_rwlock_read_lock() solves the race condition, > I'm afraid that it would be too expensive in case when logging is off, since it introduces > acquiring and releasing lock into the main flow of ring updates. Actually my v2 fixes the performance penalty when logging is off. The lock is now taken after the logging feature check. But still, I agree logging on case will suffer from a performance penalty. > It is OK for now, as it fixes the bug, but we need to perform more careful performance measurements, > and see whether the performance degradation is not too prohibitive. > > As alternative, we may consider using more light weighted busy looping. I think it will end up almost being the same, as both threads will need to busy loop. PMD thread to be sure the protocol thread isn't being unmapping the region before doing the logging, and protocol thread to be sure the PMD thread is not doing logging before handling the set log base. Maybe you have something else in mind? > Also, lets fix by this series the __sync_fetch_and_or_8 -> __sync_fetch_and_or, > as it may improve the performance slightly. Sure, this can be done, but it would need to be benchmarked first. Regards, Maxime