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

Jiri Pirko
2024-05-20T12:48:21Z

Fri, May 10, 2024 at 09:11:16AM CEST, hengqi@linux.alibaba.com wrote:
>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.

But when the device does not support dim, the orphan mode is still
needed, isn't it?

>
>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
>>
>>