From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41178) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bVb1M-0005QJ-EH for qemu-devel@nongnu.org; Fri, 05 Aug 2016 05:02:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bVb1I-0002ZC-78 for qemu-devel@nongnu.org; Fri, 05 Aug 2016 05:02:23 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:44600) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bVb1H-0002YZ-Ve for qemu-devel@nongnu.org; Fri, 05 Aug 2016 05:02:20 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u758xRAY140901 for ; Fri, 5 Aug 2016 05:02:18 -0400 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0a-001b2d01.pphosted.com with ESMTP id 24knge75j8-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 05 Aug 2016 05:02:18 -0400 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 5 Aug 2016 10:02:15 +0100 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id C7E2117D8024 for ; Fri, 5 Aug 2016 10:03:49 +0100 (BST) Received: from d06av05.portsmouth.uk.ibm.com (d06av05.portsmouth.uk.ibm.com [9.149.37.229]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u7592CfA66191384 for ; Fri, 5 Aug 2016 09:02:12 GMT Received: from d06av05.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av05.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u7592CNq004778 for ; Fri, 5 Aug 2016 03:02:12 -0600 Date: Fri, 5 Aug 2016 11:02:11 +0200 From: Cornelia Huck In-Reply-To: <20160804225038-mutt-send-email-mst@kernel.org> References: <1470266160-17896-1-git-send-email-mst@redhat.com> <20160804093515.05627a95.cornelia.huck@de.ibm.com> <20160804225038-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20160805110211.385ae55b.cornelia.huck@de.ibm.com> Subject: Re: [Qemu-devel] [PATCH] virtio-net: allow increasing rx queue size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, Jason Wang On Thu, 4 Aug 2016 22:52:29 +0300 "Michael S. Tsirkin" wrote: > On Thu, Aug 04, 2016 at 09:35:15AM +0200, Cornelia Huck wrote: > > On Thu, 4 Aug 2016 02:16:14 +0300 > > "Michael S. Tsirkin" wrote: > > > > > This allows increasing the rx queue size up to 1024: unlike with tx, > > > guests don't put in huge S/G lists into RX so the risk of running into > > > the max 1024 limitation due to some off-by-one seems small. > > > > > > It's helpful for users like OVS-DPDK which don't do any buffering on the > > > host - 1K roughly matches 500 entries in tun + 256 in the current rx > > > queue, which seems to work reasonably well. We could probably make do > > > with ~750 entries but virtio spec limits us to powers of two. > > > It might be a good idea to specify an s/g size limit in a future > > > version. > > > > > > It also might be possible to make the queue size smaller down the road, 64 > > > seems like the minimal value which will still work (as guests seem to > > > assume a queue full of 1.5K buffers is enough to process the largest > > > incoming packet, which is ~64K). No one actually asked for this, and > > > with virtio 1 guests can reduce ring size without need for host > > > configuration, so don't bother with this for now. > > > > Do we need some kind of sanity check that the guest did not resize > > below a reasonable limit? > > Unfortunately the spec does not have an interface for that. > Guests expect they can get away with any size. Might be a good idea to add this in the future, so that the guest is able to discover the minimum and the host can refuse to work if the configured queue is too small. (I can easily reject the setup ccw on virtio-ccw, but is there an elegant way to refuse setting up the queues with virtio-pci?) > > > > > > > Signed-off-by: Michael S. Tsirkin > > > --- > > > include/hw/virtio/virtio-net.h | 1 + > > > hw/net/virtio-net.c | 22 +++++++++++++++++++++- > > > 2 files changed, 22 insertions(+), 1 deletion(-) > > > > > > > > > > @@ -1716,10 +1717,28 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp) > > > VirtIONet *n = VIRTIO_NET(dev); > > > NetClientState *nc; > > > int i; > > > + int min_rx_queue_size; > > > > > > virtio_net_set_config_size(n, n->host_features); > > > virtio_init(vdev, "virtio-net", VIRTIO_ID_NET, n->config_size); > > > > > > + /* > > > + * We set a lower limit on RX queue size to what it always was. > > > + * Guests that want a smaller ring can always resize it without > > > + * help from us (using virtio 1 and up). > > > + */ > > > + min_rx_queue_size = 256; > > > > I'd find it more readable to introduce a #define with the old queue > > size as the minimum size... > > > > > + if (n->net_conf.rx_queue_size < min_rx_queue_size || > > > + n->net_conf.rx_queue_size > VIRTQUEUE_MAX_SIZE || > > > + (n->net_conf.rx_queue_size & (n->net_conf.rx_queue_size - 1))) { > > > + error_setg(errp, "Invalid rx_queue_size (= %" PRIu16 "), " > > > + "must be a power of 2 between %d and %d.", > > > + n->net_conf.rx_queue_size, min_rx_queue_size, > > > + VIRTQUEUE_MAX_SIZE); > > > + virtio_cleanup(vdev); > > > + return; > > > + } > > > + > > > n->max_queues = MAX(n->nic_conf.peers.queues, 1); > > > if (n->max_queues * 2 + 1 > VIRTIO_QUEUE_MAX) { > > > error_setg(errp, "Invalid number of queues (= %" PRIu32 "), " > > > @@ -1880,6 +1899,7 @@ static Property virtio_net_properties[] = { > > > TX_TIMER_INTERVAL), > > > DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST), > > > DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx), > > > + DEFINE_PROP_UINT16("rx_queue_size", VirtIONet, net_conf.rx_queue_size, 256), > > > > ...and defaulting to that #define (or one derived from the #define > > above) here. > > These happen to be the same, but they are in fact > unrelated: one is the default, the other is the > min value. Hm... /* previously fixed value */ #define VIRTIO_NET_RX_DEFAULT_SIZE 256 /* for now, only allow larger queues; with virtio-1, guest can downsize */ #define VIRTIO_NET_RX_MIN_SIZE VIRTIO_NET_RX_DEFAULT_SIZE This would allow getting rid of the new local variable and gets us a speaking define in the property definition.