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Re: [Qemu-devel] [PATCH] virtio-net: allow increasing rx queue size
From: |
Cornelia Huck |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-net: allow increasing rx queue size |
Date: |
Thu, 4 Aug 2016 09:35:15 +0200 |
On Thu, 4 Aug 2016 02:16:14 +0300
"Michael S. Tsirkin" <address@hidden> 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?
>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> 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.
> DEFINE_PROP_END_OF_LIST(),
> };
>
Do we need compat handling for the new property?