Date: Thu, 13 Jun 2024 10:47:27 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: netdev@...r.kernel.org,
 Jason Wang <jasowang@...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 v4 08/15] virtio_net: sq support premapped mode

On Wed, 12 Jun 2024 19:41:51 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Tue, Jun 11, 2024 at 07:41:40PM +0800, Xuan Zhuo 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.
> >
> > * 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 | 219 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 215 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index e84a4624549b..4968ab7eb5a4 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>
> >
> >  static int napi_weight = NAPI_POLL_WEIGHT;
> >  module_param(napi_weight, int, 0444);
> > @@ -276,6 +277,25 @@ struct virtnet_rq_dma {
> >  	u16 need_sync;
> >  };
> >
> > +struct virtnet_sq_dma {
> > +	union {
> > +		struct virtnet_sq_dma *next;
>
> Maybe:
>
> struct llist_node node;
>
> I'd like to avoid growing our own single linked list
> implementation if at all possible.

I will fix all the comments in next version.

Thanks.


>
>
>
> > +		void *data;
> > +	};
> > +	dma_addr_t addr;
> > +	u32 len;
> > +	u8 num;
> > +};
> > +
> > +struct virtnet_sq_dma_info {
> > +	/* record for kfree */
> > +	void *p;
> > +
> > +	u32 free_num;
> > +
> > +	struct virtnet_sq_dma *free;
> > +};
> > +
> >  /* Internal representation of a send virtqueue */
> >  struct send_queue {
> >  	/* Virtqueue associated with this send _queue */
> > @@ -295,6 +315,11 @@ 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 +517,11 @@ 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,
> >  };
> >
> > -#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 +537,178 @@ 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 = p->next;
> > +	}
> > +
> > +	*data = tail->data;
> > +
> > +	tail->next = sq->dmainfo.free;
> > +	sq->dmainfo.free = head;
> > +	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 = tail->next;
> > +	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, *tail, *p;
> > +	struct scatterlist *sg;
> > +	dma_addr_t addr;
> > +	int i, err;
> > +
> > +	if (num > sq->dmainfo.free_num)
> > +		return NULL;
> > +
> > +	head = sq->dmainfo.free;
> > +	p = head;
> > +
> > +	tail = 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;
> > +
> > +		tail = p;
> > +		tail->addr = sg->dma_address;
> > +		tail->len = sg->length;
> > +
> > +		p = p->next;
> > +	}
> > +
> > +	return virtnet_dma_chain_update(sq, head, tail, num, data);
> > +
> > +err:
> > +	if (tail) {
> > +		virtnet_dma_chain_update(sq, head, tail, i, data);
> > +		virtnet_sq_unmap(sq, (void **)&head);
> > +	}
> > +
> > +	return NULL;
> > +}
> > +
> >  static int virtnet_add_outbuf(struct send_queue *sq, int num, void *data,
> >  			      enum virtnet_xmit_type type)
> >  {
> > -	return virtqueue_add_outbuf(sq->vq, sq->sg, num,
> > -				    virtnet_xmit_ptr_mix(data, type),
> > -				    GFP_ATOMIC);
> > +	int ret;
> > +
> > +	data = virtnet_xmit_ptr_mix(data, type);
> > +
> > +	if (sq->premapped) {
> > +		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->premapped) {
> > +		virtnet_xmit_ptr_strip(&data);
> > +		virtnet_sq_unmap(sq, &data);
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +static int virtnet_sq_alloc_dma_meta(struct send_queue *sq)
> > +{
> > +	struct virtnet_sq_dma *d;
> > +	int num, i;
> > +
> > +	num = virtqueue_get_vring_size(sq->vq);
> > +
> > +	/* 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, effectively limiting it to
> > +	 * twice the size of the ring buffer.
> > +	 *
> > +	 * If the kernel stack and xdp tx/redirect attempt to use more
> > +	 * descriptors than allowed by this double ring buffer size,
> > +	 * virtnet_add_outbuf() will return an -ENOMEM error. But the af-xdp can
> > +	 * work continually.
> > +	 */
> > +	if (virtio_has_feature(sq->vq->vdev, VIRTIO_RING_F_INDIRECT_DESC))
> > +		num = num * 2;
> > +
> > +	sq->dmainfo.free = kcalloc(num, sizeof(*sq->dmainfo.free), GFP_KERNEL);
>
> Can be large. kvmalloc seems more appropriate.
>
>
> > +	if (!sq->dmainfo.free)
> > +		return -ENOMEM;
> > +
> > +	sq->dmainfo.p = sq->dmainfo.free;
> > +	sq->dmainfo.free_num = num;
> > +
> > +	for (i = 0; i < num; ++i) {
> > +		d = &sq->dmainfo.free[i];
> > +		d->next = d + 1;
> > +	}
> > +
> > +	d->next = NULL;
> > +
> > +	return 0;
> > +}
> > +
> > +static void virtnet_sq_free_dma_meta(struct send_queue *sq)
> > +{
> > +	kfree(sq->dmainfo.p);
> > +
> > +	sq->dmainfo.p = NULL;
> > +	sq->dmainfo.free = NULL;
> > +	sq->dmainfo.free_num = 0;
> > +}
> > +
> > +/* This function must be called immediately after creating the vq, or after vq
> > + * reset, and before adding any buffers to it.
> > + */
> > +static int virtnet_sq_set_premapped(struct send_queue *sq, bool premapped)
> > +{
> > +	if (premapped) {
> > +		if (virtnet_sq_alloc_dma_meta(sq))
> > +			return -ENOMEM;
>
> I would just return what virtnet_sq_alloc_dma_meta returns.
> 	int r = virtnet_sq_alloc_dma_meta();
>
> 	if (r)
> 		return r;
>
> > +	} else {
> > +		virtnet_sq_free_dma_meta(sq);
> > +	}
> > +
> > +	BUG_ON(virtqueue_set_dma_premapped(sq->vq, premapped));
> > +
> > +	sq->premapped = premapped;
> > +	return 0;
> >  }
> >
> >  static void __free_old_xmit(struct send_queue *sq, bool in_napi,
> > @@ -529,6 +722,7 @@ static void __free_old_xmit(struct send_queue *sq, bool in_napi,
> >  	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> >  		++stats->packets;
> >
> > +retry:
> >  		switch (virtnet_xmit_ptr_strip(&ptr)) {
> >  		case VIRTNET_XMIT_TYPE_SKB:
> >  			skb = ptr;
> > @@ -545,6 +739,10 @@ static void __free_old_xmit(struct send_queue *sq, bool in_napi,
> >  			stats->bytes += xdp_get_frame_len(frame);
> >  			xdp_return_frame(frame);
> >  			break;
> > +
> > +		case VIRTNET_XMIT_TYPE_DMA:
> > +			virtnet_sq_unmap(sq, &ptr);
> > +			goto retry;
> >  		}
> >  	}
> >  }
> > @@ -5232,6 +5430,8 @@ 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);
> > +
> > +		virtnet_sq_free_dma_meta(&vi->sq[i]);
> >  	}
> >
> >  	/* We called __netif_napi_del(),
> > @@ -5280,6 +5480,13 @@ static void free_receive_page_frags(struct virtnet_info *vi)
> >
> >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> >  {
> > +	struct virtnet_info *vi = vq->vdev->priv;
> > +	struct send_queue *sq;
> > +	int i = vq2rxq(vq);
> > +
> > +	sq = &vi->sq[i];
> > +
> > +retry:
> >  	switch (virtnet_xmit_ptr_strip(&buf)) {
> >  	case VIRTNET_XMIT_TYPE_SKB:
> >  		dev_kfree_skb(buf);
> > @@ -5288,6 +5495,10 @@ static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> >  	case VIRTNET_XMIT_TYPE_XDP:
> >  		xdp_return_frame(buf);
> >  		break;
> > +
> > +	case VIRTNET_XMIT_TYPE_DMA:
> > +		virtnet_sq_unmap(sq, &buf);
> > +		goto retry;
>
> document what's going on here? why are we retrying?
>
>
> >  	}
> >  }
> >
> > --
> > 2.32.0.3.g01195cf9f
>

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