From mboxrd@z Thu Jan 1 00:00:00 1970 From: Asias He Subject: Re: [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path Date: Tue, 07 Aug 2012 16:50:45 +0800 Message-ID: <5020D6E5.3060504@redhat.com> 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> <20120806151731.GA23220@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120806151731.GA23220@lst.de> 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 To: Christoph Hellwig Cc: Jens Axboe , kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Tejun Heo , Shaohua Li List-Id: virtualization@lists.linuxfoundation.org On 08/06/2012 11:17 PM, Christoph Hellwig wrote: > 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. > Thanks for the explanation. V6 is in flight. -- Asias