Re: [PATCH vhost v10 10/10] virtio_net: support dma premapped

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Thu, 22 Jun 2023 08:15:03 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Fri, Jun 02, 2023 at 05:22:06PM +0800, Xuan Zhuo wrote:
> > Introduce the module param "experiment_premapped" to enable the function
> > that the virtio-net do dma mapping.
> >
> > If that is true, the vq of virtio-net is under the premapped mode.
> > It just handle the sg with dma_address. And the driver must get the dma
> > address of the buffer to unmap after get the buffer from virtio core.
> >
> > That will be useful when AF_XDP is enable, AF_XDP tx and the kernel packet
> > xmit will share the tx queue, so the skb xmit must support the premapped
> > mode.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>
>
> I put this in next but I don't think this is going upstream
> in its current form,

I agree.

> certainly not with the experiment_premapped mod config
> that no one will know how to enable. If you want to experiment,
> keep it in your private tree, experimenting on humans requires
> an ethics board approval and consent forms :)

^_^

Maybe, this patchset should not include this patch,
this patch should work with the patch that uses the premapped.

>
> Spreading the "premapped" boolean all of the place is also
> far from pretty, I wonder why we can't only specify it when adding.

I guess you mean that we just use the "premapped" for the virtio api.

I will try.

Thanks.


>
> > ---
> >  drivers/net/virtio_net.c | 163 +++++++++++++++++++++++++++++++++------
> >  1 file changed, 141 insertions(+), 22 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 2396c28c0122..5898212fcb3c 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -26,10 +26,11 @@
> >  static int napi_weight = NAPI_POLL_WEIGHT;
> >  module_param(napi_weight, int, 0444);
> >
> > -static bool csum = true, gso = true, napi_tx = true;
> > +static bool csum = true, gso = true, napi_tx = true, experiment_premapped;
> >  module_param(csum, bool, 0444);
> >  module_param(gso, bool, 0444);
> >  module_param(napi_tx, bool, 0644);
> > +module_param(experiment_premapped, bool, 0644);
> >
> >  /* FIXME: MTU in config. */
> >  #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
> > @@ -142,6 +143,9 @@ struct send_queue {
> >
> >  	/* Record whether sq is in reset state. */
> >  	bool reset;
> > +
> > +	/* The vq is premapped mode. */
> > +	bool premapped;
> >  };
> >
> >  /* Internal representation of a receive virtqueue */
> > @@ -174,6 +178,9 @@ struct receive_queue {
> >  	char name[16];
> >
> >  	struct xdp_rxq_info xdp_rxq;
> > +
> > +	/* The vq is premapped mode. */
> > +	bool premapped;
> >  };
> >
> >  /* This structure can contain rss message with maximum settings for indirection table and keysize
> > @@ -546,6 +553,105 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> >  	return skb;
> >  }
> >
> > +static int virtnet_generic_unmap(struct virtqueue *vq, struct virtqueue_detach_cursor *cursor)
> > +{
> > +	enum dma_data_direction dir;
> > +	dma_addr_t addr;
> > +	u32 len;
> > +	int err;
> > +
> > +	do {
> > +		err = virtqueue_detach(vq, cursor, &addr, &len, &dir);
> > +		if (!err || err == -EAGAIN)
> > +			dma_unmap_page_attrs(virtqueue_dma_dev(vq), addr, len, dir, 0);
> > +
> > +	} while (err == -EAGAIN);
> > +
> > +	return err;
> > +}
> > +
> > +static void *virtnet_detach_unused_buf(struct virtqueue *vq, bool premapped)
> > +{
> > +	struct virtqueue_detach_cursor cursor;
> > +	void *buf;
> > +
> > +	if (!premapped)
> > +		return virtqueue_detach_unused_buf(vq);
> > +
> > +	buf = virtqueue_detach_unused_buf_premapped(vq, &cursor);
> > +	if (buf)
> > +		virtnet_generic_unmap(vq, &cursor);
> > +
> > +	return buf;
> > +}
> > +
> > +static void *virtnet_get_buf_ctx(struct virtqueue *vq, bool premapped, u32 *len, void **ctx)
> > +{
> > +	struct virtqueue_detach_cursor cursor;
> > +	void *buf;
> > +
> > +	if (!premapped)
> > +		return virtqueue_get_buf_ctx(vq, len, ctx);
> > +
> > +	buf = virtqueue_get_buf_premapped(vq, len, ctx, &cursor);
> > +	if (buf)
> > +		virtnet_generic_unmap(vq, &cursor);
> > +
> > +	return buf;
> > +}
> > +
> > +#define virtnet_rq_get_buf(rq, plen, pctx) \
> > +({ \
> > +	typeof(rq) _rq = (rq); \
> > +	virtnet_get_buf_ctx(_rq->vq, _rq->premapped, plen, pctx); \
> > +})
> > +
> > +#define virtnet_sq_get_buf(sq, plen, pctx) \
> > +({ \
> > +	typeof(sq) _sq = (sq); \
> > +	virtnet_get_buf_ctx(_sq->vq, _sq->premapped, plen, pctx); \
> > +})
> > +
> > +static int virtnet_add_sg(struct virtqueue *vq, bool premapped,
> > +			  struct scatterlist *sg, unsigned int num, bool out,
> > +			  void *data, void *ctx, gfp_t gfp)
> > +{
> > +	enum dma_data_direction dir;
> > +	struct device *dev;
> > +	int err, ret;
> > +
> > +	if (!premapped)
> > +		return virtqueue_add_sg(vq, sg, num, out, data, ctx, gfp);
> > +
> > +	dir = out ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
> > +	dev = virtqueue_dma_dev(vq);
> > +
> > +	ret = dma_map_sg_attrs(dev, sg, num, dir, 0);
> > +	if (ret != num)
> > +		goto err;
> > +
> > +	err = virtqueue_add_sg(vq, sg, num, out, data, ctx, gfp);
> > +	if (err < 0)
> > +		goto err;
> > +
> > +	return 0;
> > +
> > +err:
> > +	dma_unmap_sg_attrs(dev, sg, num, dir, 0);
> > +	return -ENOMEM;
> > +}
> > +
> > +static int virtnet_add_outbuf(struct send_queue *sq, unsigned int num, void *data)
> > +{
> > +	return virtnet_add_sg(sq->vq, sq->premapped, sq->sg, num, true, data, NULL, GFP_ATOMIC);
> > +}
> > +
> > +static int virtnet_add_inbuf(struct receive_queue *rq, unsigned int num, void *data,
> > +			     void *ctx, gfp_t gfp)
> > +{
> > +	return virtnet_add_sg(rq->vq, rq->premapped, rq->sg, num, false, data, ctx, gfp);
> > +}
> > +
> >  static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
> >  {
> >  	unsigned int len;
> > @@ -553,7 +659,7 @@ static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
> >  	unsigned int bytes = 0;
> >  	void *ptr;
> >
> > -	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> > +	while ((ptr = virtnet_sq_get_buf(sq, &len, NULL)) != NULL) {
> >  		if (likely(!is_xdp_frame(ptr))) {
> >  			struct sk_buff *skb = ptr;
> >
> > @@ -667,8 +773,7 @@ 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 */
> >
> > @@ -744,7 +849,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> >  	}
> >
> >  	/* Free up any pending old buffers before queueing new ones. */
> > -	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> > +	while ((ptr = virtnet_sq_get_buf(sq, &len, NULL)) != NULL) {
> >  		if (likely(is_xdp_frame(ptr))) {
> >  			struct xdp_frame *frame = ptr_to_xdp(ptr);
> >
> > @@ -828,7 +933,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> >  		void *buf;
> >  		int off;
> >
> > -		buf = virtqueue_get_buf(rq->vq, &buflen);
> > +		buf = virtnet_rq_get_buf(rq, &buflen, NULL);
> >  		if (unlikely(!buf))
> >  			goto err_buf;
> >
> > @@ -1119,7 +1224,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> >  		return -EINVAL;
> >
> >  	while (--*num_buf > 0) {
> > -		buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> > +		buf = virtnet_rq_get_buf(rq, &len, &ctx);
> >  		if (unlikely(!buf)) {
> >  			pr_debug("%s: rx error: %d buffers out of %d missing\n",
> >  				 dev->name, *num_buf,
> > @@ -1344,7 +1449,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> >  	while (--num_buf) {
> >  		int num_skb_frags;
> >
> > -		buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> > +		buf = virtnet_rq_get_buf(rq, &len, &ctx);
> >  		if (unlikely(!buf)) {
> >  			pr_debug("%s: rx error: %d buffers out of %d missing\n",
> >  				 dev->name, num_buf,
> > @@ -1407,7 +1512,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> >  err_skb:
> >  	put_page(page);
> >  	while (num_buf-- > 1) {
> > -		buf = virtqueue_get_buf(rq->vq, &len);
> > +		buf = virtnet_rq_get_buf(rq, &len, NULL);
> >  		if (unlikely(!buf)) {
> >  			pr_debug("%s: rx error: %d buffers missing\n",
> >  				 dev->name, num_buf);
> > @@ -1534,7 +1639,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> >  	alloc_frag->offset += len;
> >  	sg_init_one(rq->sg, buf + VIRTNET_RX_PAD + xdp_headroom,
> >  		    vi->hdr_len + GOOD_PACKET_LEN);
> > -	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > +	err = virtnet_add_inbuf(rq, 1, buf, ctx, gfp);
> >  	if (err < 0)
> >  		put_page(virt_to_head_page(buf));
> >  	return err;
> > @@ -1581,8 +1686,8 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
> >
> >  	/* chain first in list head */
> >  	first->private = (unsigned long)list;
> > -	err = virtqueue_add_inbuf(rq->vq, rq->sg, vi->big_packets_num_skbfrags + 2,
> > -				  first, gfp);
> > +	err = virtnet_add_inbuf(rq, vi->big_packets_num_skbfrags + 2,
> > +				first, NULL, gfp);
> >  	if (err < 0)
> >  		give_pages(rq, first);
> >
> > @@ -1645,7 +1750,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> >
> >  	sg_init_one(rq->sg, buf, len);
> >  	ctx = mergeable_len_to_ctx(len + room, headroom);
> > -	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > +	err = virtnet_add_inbuf(rq, 1, buf, ctx, gfp);
> >  	if (err < 0)
> >  		put_page(virt_to_head_page(buf));
> >
> > @@ -1768,13 +1873,13 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
> >  		void *ctx;
> >
> >  		while (stats.packets < budget &&
> > -		       (buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx))) {
> > +		       (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> >  			receive_buf(vi, rq, buf, len, ctx, xdp_xmit, &stats);
> >  			stats.packets++;
> >  		}
> >  	} else {
> >  		while (stats.packets < budget &&
> > -		       (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> > +		       (buf = virtnet_rq_get_buf(rq, &len, NULL)) != NULL) {
> >  			receive_buf(vi, rq, buf, len, NULL, xdp_xmit, &stats);
> >  			stats.packets++;
> >  		}
> > @@ -1984,7 +2089,7 @@ static int xmit_skb(struct send_queue *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)
> > @@ -3552,15 +3657,17 @@ static void free_unused_bufs(struct virtnet_info *vi)
> >  	int i;
> >
> >  	for (i = 0; i < vi->max_queue_pairs; i++) {
> > -		struct virtqueue *vq = vi->sq[i].vq;
> > -		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> > -			virtnet_sq_free_unused_buf(vq, buf);
> > +		struct send_queue *sq = &vi->sq[i];
> > +
> > +		while ((buf = virtnet_detach_unused_buf(sq->vq, sq->premapped)) != NULL)
> > +			virtnet_sq_free_unused_buf(sq->vq, buf);
> >  	}
> >
> >  	for (i = 0; i < vi->max_queue_pairs; i++) {
> > -		struct virtqueue *vq = vi->rq[i].vq;
> > -		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> > -			virtnet_rq_free_unused_buf(vq, buf);
> > +		struct receive_queue *rq = &vi->rq[i];
> > +
> > +		while ((buf = virtnet_detach_unused_buf(rq->vq, rq->premapped)) != NULL)
> > +			virtnet_rq_free_unused_buf(rq->vq, buf);
> >  	}
> >  }
> >
> > @@ -3658,6 +3765,18 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >  		vi->rq[i].vq = vqs[rxq2vq(i)];
> >  		vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
> >  		vi->sq[i].vq = vqs[txq2vq(i)];
> > +
> > +		if (experiment_premapped) {
> > +			if (!virtqueue_set_premapped(vi->rq[i].vq))
> > +				vi->rq[i].premapped = true;
> > +			else
> > +				netdev_warn(vi->dev, "RXQ (%d) enable premapped failure.\n", i);
> > +
> > +			if (!virtqueue_set_premapped(vi->sq[i].vq))
> > +				vi->sq[i].premapped = true;
> > +			else
> > +				netdev_warn(vi->dev, "TXQ (%d) enable premapped failure.\n", i);
> > +		}
> >  	}
> >
> >  	/* run here: ret == 0. */
> > --
> > 2.32.0.3.g01195cf9f
>
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