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Subject: Re: [virtio-dev] [PATCH] virtio-net: use mtu size as buffer length for big packets
On 8/4/2022 3:10 PM, Michael S. Tsirkin wrote:
External email: Use caution opening links or attachments On Thu, Aug 04, 2022 at 01:00:46PM +0800, Jason Wang wrote:On Tue, Aug 2, 2022 at 12:47 PM Gavin Li <gavinl@nvidia.com> wrote:Currently add_recvbuf_big() allocates MAX_SKB_FRAGS segments for big packets even when GUEST_* offloads are not present on the device. However, if GSO is not supported, it would be sufficient to allocate segments to cover just up the MTU size and no further. Allocating the maximum amount of segments results in a large waste of buffer space in the queue, which limits the number of packets that can be buffered and can result in reduced performance. Therefore, if GSO is not supported, use the MTU to calculate the optimal amount of segments required. Below is the iperf TCP test results over a Mellanox NIC, using vDPA for 1 VQ, queue size 1024, before and after the change, with the iperf server running over the virtio-net interface. MTU(Bytes)/Bandwidth (Gbit/s) Before After 1500 22.5 22.4 9000 12.8 25.9 Signed-off-by: Gavin Li <gavinl@nvidia.com> Reviewed-by: Gavi Teitz <gavi@nvidia.com> Reviewed-by: Parav Pandit <parav@nvidia.com> --- drivers/net/virtio_net.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index ec8e1b3108c3..d36918c1809d 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -222,6 +222,9 @@ struct virtnet_info { /* I like... big packets and I cannot lie! */ bool big_packets; + /* Indicates GSO support */ + bool gso_is_supported; + /* Host will merge rx buffers for big packets (shake it! shake it!) */ bool mergeable_rx_bufs; @@ -1312,14 +1315,21 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq, static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq, gfp_t gfp) { + unsigned int sg_num = MAX_SKB_FRAGS; struct page *first, *list = NULL; char *p; int i, err, offset; - sg_init_table(rq->sg, MAX_SKB_FRAGS + 2); + if (!vi->gso_is_supported) { + unsigned int mtu = vi->dev->mtu; + + sg_num = (mtu % PAGE_SIZE) ? mtu / PAGE_SIZE + 1 : mtu / PAGE_SIZE; + } + + sg_init_table(rq->sg, sg_num + 2); /* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */ - for (i = MAX_SKB_FRAGS + 1; i > 1; --i) { + for (i = sg_num + 1; i > 1; --i) { first = get_a_page(rq, gfp); if (!first) { if (list) @@ -1350,7 +1360,7 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq, /* chain first in list head */ first->private = (unsigned long)list; - err = virtqueue_add_inbuf(rq->vq, rq->sg, MAX_SKB_FRAGS + 2, + err = virtqueue_add_inbuf(rq->vq, rq->sg, sg_num + 2, first, gfp); if (err < 0) give_pages(rq, first); @@ -3571,8 +3581,10 @@ static int virtnet_probe(struct virtio_device *vdev) if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) || virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) || virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN) || - virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO)) + virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO)) { vi->big_packets = true; + vi->gso_is_supported = true;Why not simply re-use big_packets here? ThanksI don't get this question. The patch does use big_packets, it wants to figure out guest GSO is off so MTU limits the size. The name "gso_is_supported" is confusing, should be e.g. guest_gso.
ACK.
+ } if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) vi->mergeable_rx_bufs = true; -- 2.31.1 --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
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