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Date: Mon, 17 Jun 2024 13:00:13 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
Eugenio Pérez <eperezma@...hat.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, virtualization@...ts.linux.dev,
bpf@...r.kernel.org
Subject: Re: [PATCH net-next v5 08/15] virtio_net: sq support premapped mode
On Fri, Jun 14, 2024 at 2:39 PM Xuan Zhuo <xuanzhuo@...ux.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 when it is bound to
> af-xdp.
>
> * virtnet_sq_set_premapped(sq, true) is used to enable premapped mode.
>
> In this mode, the driver will record the dma info when skb or xdp
> frame is sent.
>
> Currently, the SQ premapped mode is operational only with af-xdp. In
> this mode, af-xdp, the kernel stack, and xdp tx/redirect will share
> the same SQ. Af-xdp independently manages its DMA. The kernel stack
> and xdp tx/redirect utilize this DMA metadata to manage the DMA
> info.
>
> If the indirect descriptor feature be supported, the volume of DMA
> details we need to maintain becomes quite substantial. Here, we have
> a cap on the amount of DMA info we manage.
>
> If the kernel stack and xdp tx/redirect attempt to use more
> descriptors, virtnet_add_outbuf() will return an -ENOMEM error. But
> the af-xdp can work continually.
Rethink of this whole logic, it looks like all the complication came
as we decided to go with a pre queue pre mapping flag. I wonder if
things could be simplified if we do that per buffer?
Then we don't need complex logic like dmainfo and cap.
>
> * virtnet_sq_set_premapped(sq, false) is used to disable premapped mode.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/net/virtio_net.c | 228 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 224 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e84a4624549b..88ab9ea1646f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -25,6 +25,7 @@
> #include <net/net_failover.h>
> #include <net/netdev_rx_queue.h>
> #include <net/netdev_queues.h>
> +#include <uapi/linux/virtio_ring.h>
Why do we need this?
>
> static int napi_weight = NAPI_POLL_WEIGHT;
> module_param(napi_weight, int, 0444);
> @@ -276,6 +277,26 @@ struct virtnet_rq_dma {
> u16 need_sync;
> };
>
> +struct virtnet_sq_dma {
> + union {
> + struct llist_node node;
> + struct llist_head head;
If we want to cap the #dmas, could we simply use an array instead of
the list here?
> + void *data;
> + };
> + dma_addr_t addr;
> + u32 len;
> + u8 num;
> +};
> +
> +struct virtnet_sq_dma_info {
> + /* record for kfree */
> + void *p;
> +
> + u32 free_num;
> +
> + struct llist_head free;
> +};
> +
> /* Internal representation of a send virtqueue */
> struct send_queue {
> /* Virtqueue associated with this send _queue */
> @@ -295,6 +316,11 @@ struct send_queue {
>
> /* Record whether sq is in reset state. */
> bool reset;
> +
> + /* SQ is premapped mode or not. */
> + bool premapped;
> +
> + struct virtnet_sq_dma_info dmainfo;
> };
>
> /* Internal representation of a receive virtqueue */
> @@ -492,9 +518,11 @@ static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> enum virtnet_xmit_type {
> VIRTNET_XMIT_TYPE_SKB,
> VIRTNET_XMIT_TYPE_XDP,
> + VIRTNET_XMIT_TYPE_DMA,
I think the name is confusing, how about TYPE_PREMAPPED?
> };
>
> -#define VIRTNET_XMIT_TYPE_MASK (VIRTNET_XMIT_TYPE_SKB | VIRTNET_XMIT_TYPE_XDP)
> +#define VIRTNET_XMIT_TYPE_MASK (VIRTNET_XMIT_TYPE_SKB | VIRTNET_XMIT_TYPE_XDP \
> + | VIRTNET_XMIT_TYPE_DMA)
>
> static enum virtnet_xmit_type virtnet_xmit_ptr_strip(void **ptr)
> {
> @@ -510,12 +538,180 @@ static void *virtnet_xmit_ptr_mix(void *ptr, enum virtnet_xmit_type type)
> return (void *)((unsigned long)ptr | type);
> }
>
> +static void virtnet_sq_unmap(struct send_queue *sq, void **data)
> +{
> + struct virtnet_sq_dma *head, *tail, *p;
> + int i;
> +
> + head = *data;
> +
> + p = head;
> +
> + for (i = 0; i < head->num; ++i) {
> + virtqueue_dma_unmap_page_attrs(sq->vq, p->addr, p->len,
> + DMA_TO_DEVICE, 0);
> + tail = p;
> + p = llist_entry(llist_next(&p->node), struct virtnet_sq_dma, node);
> + }
> +
> + *data = tail->data;
> +
> + __llist_add_batch(&head->node, &tail->node, &sq->dmainfo.free);
> +
> + sq->dmainfo.free_num += head->num;
> +}
> +
> +static void *virtnet_dma_chain_update(struct send_queue *sq,
> + struct virtnet_sq_dma *head,
> + struct virtnet_sq_dma *tail,
> + u8 num, void *data)
> +{
> + sq->dmainfo.free_num -= num;
> + head->num = num;
> +
> + tail->data = data;
> +
> + return virtnet_xmit_ptr_mix(head, VIRTNET_XMIT_TYPE_DMA);
> +}
> +
> +static struct virtnet_sq_dma *virtnet_sq_map_sg(struct send_queue *sq, int num, void *data)
> +{
> + struct virtnet_sq_dma *head = NULL, *p = NULL;
> + struct scatterlist *sg;
> + dma_addr_t addr;
> + int i, err;
> +
> + if (num > sq->dmainfo.free_num)
> + return NULL;
> +
> + for (i = 0; i < num; ++i) {
> + sg = &sq->sg[i];
> +
> + addr = virtqueue_dma_map_page_attrs(sq->vq, sg_page(sg),
> + sg->offset,
> + sg->length, DMA_TO_DEVICE,
> + 0);
> + err = virtqueue_dma_mapping_error(sq->vq, addr);
> + if (err)
> + goto err;
> +
> + sg->dma_address = addr;
> +
> + p = llist_entry(llist_del_first(&sq->dmainfo.free),
> + struct virtnet_sq_dma, node);
> +
> + p->addr = sg->dma_address;
> + p->len = sg->length;
I may miss something, but I don't see how we cap the total number of dmainfos.
Thanks
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