From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53034) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YIZ3k-0001KV-0r for qemu-devel@nongnu.org; Tue, 03 Feb 2015 03:42:16 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YIZ3h-0004va-4m for qemu-devel@nongnu.org; Tue, 03 Feb 2015 03:42:11 -0500 Received: from mail-wi0-x235.google.com ([2a00:1450:400c:c05::235]:38590) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YIZ3g-0004vP-O1 for qemu-devel@nongnu.org; Tue, 03 Feb 2015 03:42:09 -0500 Received: by mail-wi0-f181.google.com with SMTP id fb4so20082581wid.2 for ; Tue, 03 Feb 2015 00:42:08 -0800 (PST) Sender: Paolo Bonzini Message-ID: <54D089DB.1040009@redhat.com> Date: Tue, 03 Feb 2015 09:42:03 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <54D032FB.404@huawei.com> In-Reply-To: <54D032FB.404@huawei.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [question] the patch which affect performance of virtio-scsi List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Wangting (Kathy)" Cc: qemu-devel On 03/02/2015 03:31, Wangting (Kathy) wrote: > Hi Paolo, > > Recently I test IO performance with virtio-scsi, and find out that the patch of > "virtio-scsi: add support for the any_layout feature" affects IO performance of model > with 4KB 32iodepth sequence read. > > Why cdb and sense is removed from the struct of VirtIOSCSICmdReq and VirtIOSCSICmdResp? Because I could not find any other way to implement ANY_LAYOUT, and virtio 1.0 requires that feature. The performance however was already improved in commit faf1e1f (virtio-scsi: Optimize virtio_scsi_init_req, 2014-09-16). Paolo > How do you consider the impact of the changes to the performance? > Although the latest version of qemu can optimize the performance by the way of reading merger, > I think the affect of this patch cannot be ignored.