Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754143Ab2HBGlD (ORCPT ); Thu, 2 Aug 2012 02:41:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27441 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751237Ab2HBGlA (ORCPT ); Thu, 2 Aug 2012 02:41:00 -0400 Message-ID: <501A2178.3000906@redhat.com> Date: Thu, 02 Aug 2012 14:43:04 +0800 From: Asias He User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Christoph Hellwig CC: linux-kernel@vger.kernel.org, Rusty Russell , Jens Axboe , Tejun Heo , Shaohua Li , "Michael S. Tsirkin" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path References: <1343888757-25723-1-git-send-email-asias@redhat.com> <1343888757-25723-5-git-send-email-asias@redhat.com> <20120802062742.GA23573@lst.de> In-Reply-To: <20120802062742.GA23573@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1527 Lines: 44 On 08/02/2012 02:27 PM, Christoph Hellwig wrote: > On Thu, Aug 02, 2012 at 02:25:56PM +0800, Asias He wrote: >> We need to support both REQ_FLUSH and REQ_FUA for bio based path since >> it does not get the sequencing of REQ_FUA into REQ_FLUSH that request >> based drivers can request. >> >> REQ_FLUSH is emulated by: >> 1. Send VIRTIO_BLK_T_FLUSH to device >> 2. Wait until the flush is finished > > There is no need to wait for the flush to finish if the REQ_FLUSH > request has no data payload. > > Even if it has a payload waiting is highly suboptimal and it should > use a non-blocking sequencing like it is done in the request layer. So, for REQ_FLUSH, what we need is that send out the VIRTIO_BLK_T_FLUSH and not to wait. >> >> REQ_FUA is emulated by: >> 1. Send the actual write >> 2. Wait until the actual write is finished >> 3. Send VIRTIO_BLK_T_FLUSH to device >> 4. Wait until the flush is finished >> 5. Signal the end of the write to upper layer > > The same comment about not blocking applies here as well. We still need to wait until the actual write is finished here? Like, REQ_FUA is emulated by: 1. Send the actual write 2. Wait until the actual write is finished 3. Send VIRTIO_BLK_T_FLUSH to device 4. Signal the end of the write to upper layer -- Asias -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/