From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46628) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YJgNM-00011x-5j for qemu-devel@nongnu.org; Fri, 06 Feb 2015 05:43:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YJgNH-0003VY-Si for qemu-devel@nongnu.org; Fri, 06 Feb 2015 05:43:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50890) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YJgNH-0003VT-Jd for qemu-devel@nongnu.org; Fri, 06 Feb 2015 05:42:59 -0500 Date: Fri, 6 Feb 2015 10:42:48 +0000 From: Stefan Hajnoczi Message-ID: <20150206104248.GD28079@stefanha-thinkpad.redhat.com> References: <54CBF2B2.20703@kamp.de> <20150205140029.GF19277@stefanha-thinkpad.redhat.com> <54D37E3D.7060208@kamp.de> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="EP0wieDxd4TSJjHq" Content-Disposition: inline In-Reply-To: <54D37E3D.7060208@kamp.de> Subject: Re: [Qemu-devel] value of VIRTQUEUE_MAX_SIZE List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: Kevin Wolf , "Michael S. Tsirkin" , Stefan Hajnoczi , ming.lei@canonical.com, "qemu-devel@nongnu.org" , Max Reitz --EP0wieDxd4TSJjHq Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Feb 05, 2015 at 03:29:17PM +0100, Peter Lieven wrote: > Am 05.02.2015 um 15:00 schrieb Stefan Hajnoczi: > >On Fri, Jan 30, 2015 at 10:08:02PM +0100, Peter Lieven wrote: > >>Just wondering if VIRTQUEUE_MAX_SIZE in include/hw/virtio/virtio.h shou= ld not be equal to IOV_MAX instead of the hardcoded 1024? > >The vring queue size is guest-visible to some extent (e.g. vring memory > >layout). Tying it to a constant that is defined by the host operating > >system could lead to problems (e.g. live migration between different > >hosts). > > > >Anyway, all of the virtio devices have a queue size that is less than or > >equal to VIRTQUEUE_MAX_SIZE (and there is an assertion to check this in > >virtio_add_queue()). > > > >Guests are supposed to honor the vring queue size, although indirect > >descriptors seem to be able to use up to VIRTQUEUE_MAX_SIZE according to > >my understanding of QEMU's virtio.c code. > > > >Why would you like to use IOV_MAX? >=20 > The idea was that IOV_MAX is the limit in case of at least virtio-blk. Th= e host > will not support more than IOV_MAX iovecs passed to a block request. Is there an issue in practice? Stefan --EP0wieDxd4TSJjHq Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJU1JqoAAoJEJykq7OBq3PI54AH/36tsb1cDDa3Uv/q4ihtwVWx elDPi+CAVj4aIjlTLVNgeEXGkadeAXwgmJUydNjFmUOvFXDCM5qTXFzEFq+7xQ1J hoGuMq9phR8qjsHbciy++xagPfQwhjg5WUlNKlQmwuPfRnzrXN3hgvteA8tUUhqY bs3TAYUZSJ0AOEeG0/wwNwIhUgwiBvhq5zfcmK6/jKLnb/qi4V4fEFHLIePz1MmD 5IuNmVsjzK5OFF+GDmkSubOfM5hLw2zELIzwfDuE59pantirdwundYlDEgtzLxdQ lpkfmzMX0/yIqo/7pe7UtKCBxpq3xfjN8bwU4fl//aNJPFrmvDaisYYUshMcDU8= =hsTZ -----END PGP SIGNATURE----- --EP0wieDxd4TSJjHq--