Re: [patch net-next] virtio_net: add support for Byte Queue Limits

Michael S. Tsirkin
2024-05-09T12:41:49Z

On Thu, May 09, 2024 at 01:46:15PM +0200, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@nvidia.com>
>
> Add support for Byte Queue Limits (BQL).
>
> Signed-off-by: Jiri Pirko <jiri@nvidia.com>

Can we get more detail on the benefits you observe etc?
Thanks!

> ---
> drivers/net/virtio_net.c | 33 ++++++++++++++++++++-------------
> 1 file changed, 20 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 218a446c4c27..c53d6dc6d332 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -84,7 +84,9 @@ struct virtnet_stat_desc {
>
> struct virtnet_sq_free_stats {
> u64 packets;
> + u64 xdp_packets;
> u64 bytes;
> + u64 xdp_bytes;
> };
>
> struct virtnet_sq_stats {
> @@ -512,19 +514,19 @@ static void __free_old_xmit(struct send_queue *sq, bool in_napi,
> void *ptr;
>
> while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> - ++stats->packets;
> -
> if (!is_xdp_frame(ptr)) {
> struct sk_buff *skb = ptr;
>
> pr_debug("Sent skb %p\n", skb);
>
> + stats->packets++;
> stats->bytes += skb->len;
> napi_consume_skb(skb, in_napi);
> } else {
> struct xdp_frame *frame = ptr_to_xdp(ptr);
>
> - stats->bytes += xdp_get_frame_len(frame);
> + stats->xdp_packets++;
> + stats->xdp_bytes += xdp_get_frame_len(frame);
> xdp_return_frame(frame);
> }
> }
> @@ -965,7 +967,8 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> virtnet_rq_free_buf(vi, rq, buf);
> }
>
> -static void free_old_xmit(struct send_queue *sq, bool in_napi)
> +static void free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
> + bool in_napi)
> {
> struct virtnet_sq_free_stats stats = {0};
>
> @@ -974,9 +977,11 @@ static void free_old_xmit(struct send_queue *sq, bool in_napi)
> /* Avoid overhead when no packets have been processed
> * happens when called speculatively from start_xmit.
> */
> - if (!stats.packets)
> + if (!stats.packets && !stats.xdp_packets)
> return;
>
> + netdev_tx_completed_queue(txq, stats.packets, stats.bytes);
> +
> u64_stats_update_begin(&sq->stats.syncp);
> u64_stats_add(&sq->stats.bytes, stats.bytes);
> u64_stats_add(&sq->stats.packets, stats.packets);
> @@ -1013,13 +1018,15 @@ static void check_sq_full_and_disable(struct virtnet_info *vi,
> * early means 16 slots are typically wasted.
> */
> if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
> - netif_stop_subqueue(dev, qnum);
> + struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
> +
> + netif_tx_stop_queue(txq);
> if (use_napi) {
> if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
> virtqueue_napi_schedule(&sq->napi, sq->vq);
> } else if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> /* More just got used, free them then recheck. */
> - free_old_xmit(sq, false);
> + free_old_xmit(sq, txq, false);
> if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
> netif_start_subqueue(dev, qnum);
> virtqueue_disable_cb(sq->vq);
> @@ -2319,7 +2326,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
>
> do {
> virtqueue_disable_cb(sq->vq);
> - free_old_xmit(sq, true);
> + free_old_xmit(sq, txq, true);
> } while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>
> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> @@ -2471,7 +2478,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> txq = netdev_get_tx_queue(vi->dev, index);
> __netif_tx_lock(txq, raw_smp_processor_id());
> virtqueue_disable_cb(sq->vq);
> - free_old_xmit(sq, true);
> + free_old_xmit(sq, txq, true);
>
> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> netif_tx_wake_queue(txq);
> @@ -2553,7 +2560,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> struct send_queue *sq = &vi->sq[qnum];
> int err;
> struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
> - bool kick = !netdev_xmit_more();
> + bool xmit_more = netdev_xmit_more();
> bool use_napi = sq->napi.weight;
>
> /* Free up any pending old buffers before queueing new ones. */
> @@ -2561,9 +2568,9 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> if (use_napi)
> virtqueue_disable_cb(sq->vq);
>
> - free_old_xmit(sq, false);
> + free_old_xmit(sq, txq, false);
>
> - } while (use_napi && kick &&
> + } while (use_napi && !xmit_more &&
> unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>
> /* timestamp packet in software */
> @@ -2592,7 +2599,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>
> check_sq_full_and_disable(vi, dev, sq);
>
> - if (kick || netif_xmit_stopped(txq)) {
> + if (__netdev_tx_sent_queue(txq, skb->len, xmit_more)) {
> if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
> u64_stats_update_begin(&sq->stats.syncp);
> u64_stats_inc(&sq->stats.kicks);
> --
> 2.44.0