Re: [PATCH net-next v2 08/21] virtio_net: sq support premapped mode

Jason Wang
2023-11-09T06:37:54Z

On Tue, Nov 7, 2023 at 11:12 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> If the xsk is enabling, the xsk tx will share the send queue.
> But the xsk requires that the send queue use the premapped mode.
> So the send queue must support premapped mode.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
> drivers/net/virtio/main.c | 163 ++++++++++++++++++++++++++++----
> drivers/net/virtio/virtio_net.h | 16 ++++
> 2 files changed, 163 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> index 16e75c08639e..f052db459156 100644
> --- a/drivers/net/virtio/main.c
> +++ b/drivers/net/virtio/main.c
> @@ -46,6 +46,7 @@ module_param(napi_tx, bool, 0644);
> #define VIRTIO_XDP_REDIR BIT(1)
>
> #define VIRTIO_XDP_FLAG BIT(0)
> +#define VIRTIO_XMIT_DATA_MASK (VIRTIO_XDP_FLAG)
>
> #define VIRTNET_DRIVER_VERSION "1.0.0"
>
> @@ -167,6 +168,29 @@ static struct xdp_frame *ptr_to_xdp(void *ptr)
> return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> }
>
> +static inline void *virtnet_sq_unmap(struct virtnet_sq *sq, void *data)
> +{
> + struct virtnet_sq_dma *next, *head;
> +
> + head = (void *)((unsigned long)data & ~VIRTIO_XMIT_DATA_MASK);
> +
> + data = head->data;
> +
> + while (head) {
> + virtqueue_dma_unmap_single_attrs(sq->vq, head->addr, head->len,
> + DMA_TO_DEVICE, 0);
> +
> + next = head->next;
> +
> + head->next = sq->dmainfo.free;
> + sq->dmainfo.free = head;
> +
> + head = next;
> + }
> +
> + return data;
> +}
> +
> static void __free_old_xmit(struct virtnet_sq *sq, bool in_napi,
> u64 *bytes, u64 *packets)
> {
> @@ -175,14 +199,24 @@ static void __free_old_xmit(struct virtnet_sq *sq, bool in_napi,
>
> while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> if (!is_xdp_frame(ptr)) {
> - struct sk_buff *skb = ptr;
> + struct sk_buff *skb;
> +
> + if (sq->do_dma)
> + ptr = virtnet_sq_unmap(sq, ptr);
> +
> + skb = ptr;
>
> pr_debug("Sent skb %p\n", skb);
>
> *bytes += skb->len;
> napi_consume_skb(skb, in_napi);
> } else {
> - struct xdp_frame *frame = ptr_to_xdp(ptr);
> + struct xdp_frame *frame;
> +
> + if (sq->do_dma)
> + ptr = virtnet_sq_unmap(sq, ptr);
> +
> + frame = ptr_to_xdp(ptr);
>
> *bytes += xdp_get_frame_len(frame);
> xdp_return_frame(frame);
> @@ -567,22 +601,104 @@ static void *virtnet_rq_alloc(struct virtnet_rq *rq, u32 size, gfp_t gfp)
> return buf;
> }
>
> -static void virtnet_rq_set_premapped(struct virtnet_info *vi)
> +static int virtnet_sq_set_premapped(struct virtnet_sq *sq)
> {
> - int i;
> + struct virtnet_sq_dma *d;
> + int err, size, i;
>
> - /* disable for big mode */
> - if (!vi->mergeable_rx_bufs && vi->big_packets)
> - return;
> + size = virtqueue_get_vring_size(sq->vq);
> +
> + size += MAX_SKB_FRAGS + 2;

Btw, the dmainfo seems per sg? If I'm correct, how can vq_size +
MAX_SKB_FRAGS + 2 work?

> +
> + sq->dmainfo.head = kcalloc(size, sizeof(*sq->dmainfo.head), GFP_KERNEL);
> + if (!sq->dmainfo.head)
> + return -ENOMEM;
> +
> + err = virtqueue_set_dma_premapped(sq->vq);
> + if (err) {
> + kfree(sq->dmainfo.head);
> + return err;
> + }

Allocating after set_dma_premapped() seems easier.

Btw, is there a benchmark of TX PPS just for this patch to demonstrate
the impact of the performance?

> +
> + sq->dmainfo.free = NULL;
> +
> + sq->do_dma = true;
> +
> + for (i = 0; i < size; ++i) {
> + d = &sq->dmainfo.head[i];
> +
> + d->next = sq->dmainfo.free;
> + sq->dmainfo.free = d;
> + }
> +
> + return 0;
> +}
> +
> +static void virtnet_set_premapped(struct virtnet_info *vi)
> +{
> + int i;
>
> for (i = 0; i < vi->max_queue_pairs; i++) {
> - if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> - continue;
> + virtnet_sq_set_premapped(&vi->sq[i]);
>
> - vi->rq[i].do_dma = true;
> + /* disable for big mode */
> + if (vi->mergeable_rx_bufs || !vi->big_packets) {
> + if (!virtqueue_set_dma_premapped(vi->rq[i].vq))
> + vi->rq[i].do_dma = true;

How about sticking a virtnet_rq_set_premapped() and calling it here?

It seems more clean.

Btw, the big mode support for pre mapping is still worthwhile
regardless whether or not XDP is supported. It has a page pool so we
can avoid redundant DMA map/unmap there.

> + }
> }
> }
>
> +static struct virtnet_sq_dma *virtnet_sq_map_sg(struct virtnet_sq *sq, int nents, void *data)
> +{
> + struct virtnet_sq_dma *d, *head;
> + struct scatterlist *sg;
> + int i;
> +
> + head = NULL;
> +
> + for_each_sg(sq->sg, sg, nents, i) {
> + sg->dma_address = virtqueue_dma_map_single_attrs(sq->vq, sg_virt(sg),
> + sg->length,
> + DMA_TO_DEVICE, 0);
> + if (virtqueue_dma_mapping_error(sq->vq, sg->dma_address))
> + goto err;
> +
> + d = sq->dmainfo.free;
> + sq->dmainfo.free = d->next;
> +
> + d->addr = sg->dma_address;
> + d->len = sg->length;
> +
> + d->next = head;
> + head = d;
> + }
> +
> + head->data = data;
> +
> + return (void *)((unsigned long)head | ((unsigned long)data & VIRTIO_XMIT_DATA_MASK));

So head contains a pointer to data, any reason we still need to pack a
data pointer here?

> +err:
> + virtnet_sq_unmap(sq, head);
> + return NULL;
> +}
> +
> +static int virtnet_add_outbuf(struct virtnet_sq *sq, u32 num, void *data)
> +{
> + int ret;
> +
> + if (sq->do_dma) {
> + data = virtnet_sq_map_sg(sq, num, data);
> + if (!data)
> + return -ENOMEM;
> + }
> +
> + ret = virtqueue_add_outbuf(sq->vq, sq->sg, num, data, GFP_ATOMIC);
> + if (ret && sq->do_dma)
> + virtnet_sq_unmap(sq, data);
> +
> + return ret;
> +}
> +
> static void free_old_xmit(struct virtnet_sq *sq, bool in_napi)
> {
> u64 bytes, packets = 0;
> @@ -686,8 +802,7 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
> skb_frag_size(frag), skb_frag_off(frag));
> }
>
> - err = virtqueue_add_outbuf(sq->vq, sq->sg, nr_frags + 1,
> - xdp_to_ptr(xdpf), GFP_ATOMIC);
> + err = virtnet_add_outbuf(sq, nr_frags + 1, xdp_to_ptr(xdpf));
> if (unlikely(err))
> return -ENOSPC; /* Caller handle free/refcnt */
>
> @@ -2126,7 +2241,8 @@ static int xmit_skb(struct virtnet_sq *sq, struct sk_buff *skb)
> return num_sg;
> num_sg++;
> }
> - return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb, GFP_ATOMIC);
> +
> + return virtnet_add_outbuf(sq, num_sg, skb);
> }
>
> static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> @@ -3818,6 +3934,8 @@ static void virtnet_free_queues(struct virtnet_info *vi)
> for (i = 0; i < vi->max_queue_pairs; i++) {
> __netif_napi_del(&vi->rq[i].napi);
> __netif_napi_del(&vi->sq[i].napi);
> +
> + kfree(vi->sq[i].dmainfo.head);
> }
>
> /* We called __netif_napi_del(),
> @@ -3866,10 +3984,23 @@ static void free_receive_page_frags(struct virtnet_info *vi)
>
> static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> {
> - if (!is_xdp_frame(buf))
> + struct virtnet_info *vi = vq->vdev->priv;
> + struct virtnet_sq *sq;
> + int i = vq2rxq(vq);
> +
> + sq = &vi->sq[i];
> +
> + if (!is_xdp_frame(buf)) {
> + if (sq->do_dma)
> + buf = virtnet_sq_unmap(sq, buf);
> +
> dev_kfree_skb(buf);
> - else
> + } else {
> + if (sq->do_dma)
> + buf = virtnet_sq_unmap(sq, buf);
> +
> xdp_return_frame(ptr_to_xdp(buf));
> + }
> }
>
> static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf)
> @@ -4075,7 +4206,7 @@ static int init_vqs(struct virtnet_info *vi)
> if (ret)
> goto err_free;
>
> - virtnet_rq_set_premapped(vi);
> + virtnet_set_premapped(vi);
>
> cpus_read_lock();
> virtnet_set_affinity(vi);
> diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> index d814341d9f97..ce806afb6d64 100644
> --- a/drivers/net/virtio/virtio_net.h
> +++ b/drivers/net/virtio/virtio_net.h
> @@ -48,6 +48,18 @@ struct virtnet_rq_dma {
> u16 need_sync;
> };
>
> +struct virtnet_sq_dma {
> + struct virtnet_sq_dma *next;
> + dma_addr_t addr;
> + u32 len;
> + void *data;

I think we need to seek a way to reuse what has been stored by virtio
core. It should be much more efficient.

Thanks

> +};
> +
> +struct virtnet_sq_dma_head {
> + struct virtnet_sq_dma *free;
> + struct virtnet_sq_dma *head;
> +};
> +
> /* Internal representation of a send virtqueue */
> struct virtnet_sq {
> /* Virtqueue associated with this virtnet_sq */
> @@ -67,6 +79,10 @@ struct virtnet_sq {
>
> /* Record whether sq is in reset state. */
> bool reset;
> +
> + bool do_dma;
> +
> + struct virtnet_sq_dma_head dmainfo;
> };
>
> /* Internal representation of a receive virtqueue */
> --
> 2.32.0.3.g01195cf9f
>