From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [119.145.14.66]) by dpdk.org (Postfix) with ESMTP id 5A8886849 for ; Thu, 11 Jun 2015 02:51:11 +0200 (CEST) Received: from 172.24.2.119 (EHLO szxeml432-hub.china.huawei.com) ([172.24.2.119]) by szxrg03-dlp.huawei.com (MOS 4.4.3-GA FastPath queued) with ESMTP id BHM68442; Thu, 11 Jun 2015 08:51:04 +0800 (CST) Received: from [127.0.0.1] (10.177.19.115) by szxeml432-hub.china.huawei.com (10.82.67.209) with Microsoft SMTP Server id 14.3.158.1; Thu, 11 Jun 2015 08:51:00 +0800 Message-ID: <5578DB72.20406@huawei.com> Date: Thu, 11 Jun 2015 08:50:58 +0800 From: Linhaifeng User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Thunderbird/31.1.0 MIME-Version: 1.0 To: Luke Gorrie , "Michael S. Tsirkin" References: <1429720392-25345-1-git-send-email-huawei.xie@intel.com> <553995DB.4000801@huawei.com> <55768FE2.5060505@huawei.com> <20150609084613.GA18121@redhat.com> In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.19.115] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020201.5578DB78.00A9, ss=1, re=0.000, recu=0.000, reip=0.000, cl=1, cld=1, fgs=0, ip=0.0.0.0, so=2013-05-26 15:14:31, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: c61f996eee8d2ada3ae1b664901a535e Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH] vhost: flush used->idx update before reading avail->flags X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 11 Jun 2015 00:51:12 -0000 On 2015/6/10 16:30, Luke Gorrie wrote: > On 9 June 2015 at 10:46, Michael S. Tsirkin wrote: > >> By the way, similarly, host side must re-check avail idx after writing >> used flags. I don't see where snabbswitch does it - is that a bug >> in snabbswitch? > > > Good question. > > Snabb Switch does not use interrupts from the guest. We always set > VRING_F_NO_NOTIFY to tell the guest that it need not interrupt us. Then we > run in poll mode and in practice check the avail ring for new descriptors > every 20us or so. Yes, host not need guest to notify when in poll mode but host also need to notify guest who use virtio_net when vring is full or emtpy.If host loss this notification guest would stop working. > > So the argument for not needing this check in both Snabb Switch and DPDK is > that we are running poll mode and don't notice whether interrupts are being > sent or not. > > Is that a solid argument or do I misunderstand what the race condition is? > > Cheers, > -Luke >