From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path Date: Mon, 6 Aug 2012 17:17:31 +0200 Message-ID: <20120806151731.GA23220@lst.de> References: <1343888757-25723-1-git-send-email-asias@redhat.com> <1343888757-25723-5-git-send-email-asias@redhat.com> <20120802062742.GA23573@lst.de> <501A2178.3000906@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jens Axboe , kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Tejun Heo , Shaohua Li , Christoph Hellwig To: Asias He Return-path: Content-Disposition: inline In-Reply-To: <501A2178.3000906@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: kvm.vger.kernel.org On Thu, Aug 02, 2012 at 02:43:04PM +0800, Asias He wrote: >> 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. If it's REQ_FLUSH without data a VIRTIO_BLK_T_FLUSH should be sent out only, if it's a REQ_FLUSH that has data a VIRTIO_BLK_T_FLUSH should be sent out, but instead of waiting for it to finish the I/O completion handler should then submit the actual write. > 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 Remove step 2 and run step 3 from the I/O completion handler.