From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Nu3Rb-0006gh-GA for qemu-devel@nongnu.org; Tue, 23 Mar 2010 08:42:51 -0400 Received: from [199.232.76.173] (port=58938 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Nu3Rb-0006gA-2V for qemu-devel@nongnu.org; Tue, 23 Mar 2010 08:42:51 -0400 Received: from Debian-exim by monty-python.gnu.org with spam-scanned (Exim 4.60) (envelope-from ) id 1Nu3Ra-00042C-1Z for qemu-devel@nongnu.org; Tue, 23 Mar 2010 08:42:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58656) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1Nu3RZ-000426-Kc for qemu-devel@nongnu.org; Tue, 23 Mar 2010 08:42:49 -0400 Date: Tue, 23 Mar 2010 14:39:16 +0200 From: "Michael S. Tsirkin" 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-Disposition: inline In-Reply-To: <1269304444.7931.68.camel@badari-desktop> Subject: [Qemu-devel] Re: [RFC] vhost-blk implementation List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Badari Pulavarty Cc: qemu-devel@nongnu.org, virtualization@lists.linux-foundation.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