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

Jiri Pirko
2024-06-05T11:30:57Z

Mon, May 20, 2024 at 02:48:15PM CEST, jiri@resnulli.us wrote:
>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?

Heng, is my assuption correct here? Thanks!

>
>>
>>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
>>>
>>>