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

Heng Qi
2024-05-10T07:12:59Z

On Thu, 9 May 2024 13:46:15 +0200, Jiri Pirko <jiri@resnulli.us> wrote:
> From: Jiri Pirko <jiri@nvidia.com>
>
> Add support for Byte Queue Limits (BQL).

Historically both Jason and Michael have attempted to support BQL
for virtio-net, for example:

https://lore.kernel.org/netdev/21384cb5-99a6-7431-1039-b356521e1bc3@redhat.com/

These discussions focus primarily on:

1. BQL is based on napi tx. Therefore, the transfer of statistical information
needs to rely on the judgment of use_napi. When the napi mode is switched to
orphan, some statistical information will be lost, resulting in temporary
inaccuracy in BQL.

2. If tx dim is supported, orphan mode may be removed and tx irq will be more
reasonable. This provides good support for BQL.

Thanks.

>
> Signed-off-by: Jiri Pirko <jiri@nvidia.com>
> ---
> 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
>
>