From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC] vhost-blk implementation Date: Tue, 23 Mar 2010 14:39:16 +0200 Message-ID: <20100323123916.GA24750@redhat.com> References: <1269304444.7931.68.camel@badari-desktop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1269304444.7931.68.camel@badari-desktop> 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: Badari Pulavarty Cc: qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Mon, Mar 22, 2010 at 05:34:04PM -0700, Badari Pulavarty wrote: > Write Results: > ============== > > I see degraded IO performance when doing sequential IO write > tests with vhost-blk compared to virtio-blk. > > # time dd of=/dev/vda if=/dev/zero bs=2M oflag=direct > > I get ~110MB/sec with virtio-blk, but I get only ~60MB/sec with > vhost-blk. Wondering why ? Try to look and number of interrupts and/or number of exits. It could also be that you are overrunning some queue. I don't see any exit mitigation strategy in your patch: when there are already lots of requests in a queue, it's usually a good idea to disable notifications and poll the queue as requests complete. That could help performance. -- MST