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

Jason Wang
2024-06-06T00:20:53Z

On Wed, Jun 5, 2024 at 7:51 PM Heng Qi <hengqi@linux.alibaba.com> wrote:
>
> On Wed, 5 Jun 2024 13:30:51 +0200, Jiri Pirko <jiri@resnulli.us> wrote:
> > 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!
> >
>
> Maybe, according to our cloud data, napi_tx=on works better than orphan mode in
> most scenarios. Although orphan mode performs better in specific benckmark,

For example pktgen (I meant even if the orphan mode can break pktgen,
it can finish when there's a new packet that needs to be sent after
pktgen is completed).

> perf of napi_tx can be enhanced through tx dim. Then, there is no reason not to
> support dim for devices that want the best performance.

Ideally, if we can drop orphan mode, everything would be simplified.

>
> Back to this patch set, I think BQL as a point that affects performance should
> deserve more comprehensive test data.

Thanks

>
> 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
> > >>>
> > >>>
>