Subject: Re: [PATCH RFC 08/13] vhost/net: convert to new API: heads->bufs

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 4 Jun 2020 05:05:42 -0400

On Wed, Jun 03, 2020 at 04:11:54PM +0800, Jason Wang wrote:
> 
> On 2020/6/2 下午9:06, Michael S. Tsirkin wrote:
> > Convert vhost net to use the new format-agnostic API.
> > In particular, don't poke at vq internals such as the
> > heads array.
> > 
> > Signed-off-by: Michael S. Tsirkin <[email-masked]>
> > ---
> >   drivers/vhost/net.c | 153 +++++++++++++++++++++++---------------------
> >   1 file changed, 81 insertions(+), 72 deletions(-)
> > 
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 749a9cf51a59..47af3d1ce3dd 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -59,13 +59,13 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
> >    * status internally; used for zerocopy tx only.
> >    */
> >   /* Lower device DMA failed */
> > -#define VHOST_DMA_FAILED_LEN	((__force __virtio32)3)
> > +#define VHOST_DMA_FAILED_LEN	(3)
> >   /* Lower device DMA done */
> > -#define VHOST_DMA_DONE_LEN	((__force __virtio32)2)
> > +#define VHOST_DMA_DONE_LEN	(2)
> >   /* Lower device DMA in progress */
> > -#define VHOST_DMA_IN_PROGRESS	((__force __virtio32)1)
> > +#define VHOST_DMA_IN_PROGRESS	(1)
> >   /* Buffer unused */
> > -#define VHOST_DMA_CLEAR_LEN	((__force __virtio32)0)
> > +#define VHOST_DMA_CLEAR_LEN	(0)
> 
> 
> Another patch for this?

It can't be a separate patch. Without switching to vhost_buf we are
passing vring_used structs around, and that has __virtio32 length. If
switching to vhost_buf, the length is u32.
Just 4 lines, not a lot would be gained by splitting it out anyway.

> 
> >   #define VHOST_DMA_IS_DONE(len) ((__force u32)(len) >= (__force u32)VHOST_DMA_DONE_LEN)
> > @@ -112,9 +112,12 @@ struct vhost_net_virtqueue {
> >   	/* last used idx for outstanding DMA zerocopy buffers */
> >   	int upend_idx;
> >   	/* For TX, first used idx for DMA done zerocopy buffers
> > -	 * For RX, number of batched heads
> > +	 * For RX, number of batched bufs
> >   	 */
> >   	int done_idx;
> > +	/* Outstanding user bufs. UIO_MAXIOV in length. */
> > +	/* TODO: we can make this smaller for sure. */
> > +	struct vhost_buf *bufs;
> >   	/* Number of XDP frames batched */
> >   	int batched_xdp;
> >   	/* an array of userspace buffers info */
> > @@ -271,6 +274,8 @@ static void vhost_net_clear_ubuf_info(struct vhost_net *n)
> >   	int i;
> >   	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
> > +		kfree(n->vqs[i].bufs);
> > +		n->vqs[i].bufs = NULL;
> >   		kfree(n->vqs[i].ubuf_info);
> >   		n->vqs[i].ubuf_info = NULL;
> >   	}
> > @@ -282,6 +287,12 @@ static int vhost_net_set_ubuf_info(struct vhost_net *n)
> >   	int i;
> >   	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
> > +		n->vqs[i].bufs = kmalloc_array(UIO_MAXIOV,
> > +					       sizeof(*n->vqs[i].bufs),
> > +					       GFP_KERNEL);
> > +		if (!n->vqs[i].bufs)
> > +			goto err;
> > +
> >   		zcopy = vhost_net_zcopy_mask & (0x1 << i);
> >   		if (!zcopy)
> >   			continue;
> > @@ -364,18 +375,18 @@ static void vhost_zerocopy_signal_used(struct vhost_net *net,
> >   	int j = 0;
> >   	for (i = nvq->done_idx; i != nvq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
> > -		if (vq->heads[i].len == VHOST_DMA_FAILED_LEN)
> > +		if (nvq->bufs[i].in_len == VHOST_DMA_FAILED_LEN)
> >   			vhost_net_tx_err(net);
> > -		if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
> > -			vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
> > +		if (VHOST_DMA_IS_DONE(nvq->bufs[i].in_len)) {
> > +			nvq->bufs[i].in_len = VHOST_DMA_CLEAR_LEN;
> >   			++j;
> >   		} else
> >   			break;
> >   	}
> >   	while (j) {
> >   		add = min(UIO_MAXIOV - nvq->done_idx, j);
> > -		vhost_add_used_and_signal_n(vq->dev, vq,
> > -					    &vq->heads[nvq->done_idx], add);
> > +		vhost_put_used_n_bufs(vq, &nvq->bufs[nvq->done_idx], add);
> > +		vhost_signal(vq->dev, vq);
> >   		nvq->done_idx = (nvq->done_idx + add) % UIO_MAXIOV;
> >   		j -= add;
> >   	}
> > @@ -390,7 +401,7 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
> >   	rcu_read_lock_bh();
> >   	/* set len to mark this desc buffers done DMA */
> > -	nvq->vq.heads[ubuf->desc].in_len = success ?
> > +	nvq->bufs[ubuf->desc].in_len = success ?
> >   		VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
> >   	cnt = vhost_net_ubuf_put(ubufs);
> > @@ -452,7 +463,8 @@ static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq)
> >   	if (!nvq->done_idx)
> >   		return;
> > -	vhost_add_used_and_signal_n(dev, vq, vq->heads, nvq->done_idx);
> > +	vhost_put_used_n_bufs(vq, nvq->bufs, nvq->done_idx);
> > +	vhost_signal(dev, vq);
> >   	nvq->done_idx = 0;
> >   }
> > @@ -558,6 +570,7 @@ static void vhost_net_busy_poll(struct vhost_net *net,
> >   static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> >   				    struct vhost_net_virtqueue *tnvq,
> > +				    struct vhost_buf *buf,
> >   				    unsigned int *out_num, unsigned int *in_num,
> >   				    struct msghdr *msghdr, bool *busyloop_intr)
> >   {
> > @@ -565,10 +578,10 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> >   	struct vhost_virtqueue *rvq = &rnvq->vq;
> >   	struct vhost_virtqueue *tvq = &tnvq->vq;
> > -	int r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
> > -				  out_num, in_num, NULL, NULL);
> > +	int r = vhost_get_avail_buf(tvq, buf, tvq->iov, ARRAY_SIZE(tvq->iov),
> > +				    out_num, in_num, NULL, NULL);
> > -	if (r == tvq->num && tvq->busyloop_timeout) {
> > +	if (!r && tvq->busyloop_timeout) {
> >   		/* Flush batched packets first */
> >   		if (!vhost_sock_zcopy(vhost_vq_get_backend(tvq)))
> >   			vhost_tx_batch(net, tnvq,
> > @@ -577,8 +590,8 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> >   		vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, false);
> > -		r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
> > -				      out_num, in_num, NULL, NULL);
> > +		r = vhost_get_avail_buf(tvq, buf, tvq->iov, ARRAY_SIZE(tvq->iov),
> > +					out_num, in_num, NULL, NULL);
> >   	}
> >   	return r;
> > @@ -607,6 +620,7 @@ static size_t init_iov_iter(struct vhost_virtqueue *vq, struct iov_iter *iter,
> >   static int get_tx_bufs(struct vhost_net *net,
> >   		       struct vhost_net_virtqueue *nvq,
> > +		       struct vhost_buf *buf,
> >   		       struct msghdr *msg,
> >   		       unsigned int *out, unsigned int *in,
> >   		       size_t *len, bool *busyloop_intr)
> > @@ -614,9 +628,9 @@ static int get_tx_bufs(struct vhost_net *net,
> >   	struct vhost_virtqueue *vq = &nvq->vq;
> >   	int ret;
> > -	ret = vhost_net_tx_get_vq_desc(net, nvq, out, in, msg, busyloop_intr);
> > +	ret = vhost_net_tx_get_vq_desc(net, nvq, buf, out, in, msg, busyloop_intr);
> > -	if (ret < 0 || ret == vq->num)
> > +	if (ret <= 0)
> >   		return ret;
> >   	if (*in) {
> > @@ -761,7 +775,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
> >   	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
> >   	struct vhost_virtqueue *vq = &nvq->vq;
> >   	unsigned out, in;
> > -	int head;
> > +	int ret;
> >   	struct msghdr msg = {
> >   		.msg_name = NULL,
> >   		.msg_namelen = 0,
> > @@ -773,6 +787,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
> >   	int err;
> >   	int sent_pkts = 0;
> >   	bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX);
> > +	struct vhost_buf buf;
> >   	do {
> >   		bool busyloop_intr = false;
> > @@ -780,13 +795,13 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
> >   		if (nvq->done_idx == VHOST_NET_BATCH)
> >   			vhost_tx_batch(net, nvq, sock, &msg);
> > -		head = get_tx_bufs(net, nvq, &msg, &out, &in, &len,
> > -				   &busyloop_intr);
> > +		ret = get_tx_bufs(net, nvq, &buf, &msg, &out, &in, &len,
> > +				  &busyloop_intr);
> >   		/* On error, stop handling until the next kick. */
> > -		if (unlikely(head < 0))
> > +		if (unlikely(ret < 0))
> >   			break;
> >   		/* Nothing new?  Wait for eventfd to tell us they refilled. */
> > -		if (head == vq->num) {
> > +		if (!ret) {
> >   			if (unlikely(busyloop_intr)) {
> >   				vhost_poll_queue(&vq->poll);
> >   			} else if (unlikely(vhost_enable_notify(&net->dev,
> > @@ -808,7 +823,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
> >   				goto done;
> >   			} else if (unlikely(err != -ENOSPC)) {
> >   				vhost_tx_batch(net, nvq, sock, &msg);
> > -				vhost_discard_vq_desc(vq, 1);
> > +				vhost_discard_avail_bufs(vq, &buf, 1);
> >   				vhost_net_enable_vq(net, vq);
> >   				break;
> >   			}
> > @@ -829,7 +844,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
> >   		/* TODO: Check specific error and bomb out unless ENOBUFS? */
> >   		err = sock->ops->sendmsg(sock, &msg, len);
> >   		if (unlikely(err < 0)) {
> > -			vhost_discard_vq_desc(vq, 1);
> > +			vhost_discard_avail_bufs(vq, &buf, 1);
> 
> 
> Do we need to decrease first_desc in vhost_discard_avail_bufs()?
> 
> 
> >   			vhost_net_enable_vq(net, vq);
> >   			break;
> >   		}
> > @@ -837,8 +852,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
> >   			pr_debug("Truncated TX packet: len %d != %zd\n",
> >   				 err, len);
> >   done:
> > -		vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
> > -		vq->heads[nvq->done_idx].len = 0;
> > +		nvq->bufs[nvq->done_idx] = buf;
> >   		++nvq->done_idx;
> >   	} while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
> > @@ -850,7 +864,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
> >   	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
> >   	struct vhost_virtqueue *vq = &nvq->vq;
> >   	unsigned out, in;
> > -	int head;
> > +	int ret;
> >   	struct msghdr msg = {
> >   		.msg_name = NULL,
> >   		.msg_namelen = 0,
> > @@ -864,6 +878,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
> >   	struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
> >   	bool zcopy_used;
> >   	int sent_pkts = 0;
> > +	struct vhost_buf buf;
> >   	do {
> >   		bool busyloop_intr;
> > @@ -872,13 +887,13 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
> >   		vhost_zerocopy_signal_used(net, vq);
> >   		busyloop_intr = false;
> > -		head = get_tx_bufs(net, nvq, &msg, &out, &in, &len,
> > -				   &busyloop_intr);
> > +		ret = get_tx_bufs(net, nvq, &buf, &msg, &out, &in, &len,
> > +				  &busyloop_intr);
> >   		/* On error, stop handling until the next kick. */
> > -		if (unlikely(head < 0))
> > +		if (unlikely(ret < 0))
> >   			break;
> >   		/* Nothing new?  Wait for eventfd to tell us they refilled. */
> > -		if (head == vq->num) {
> > +		if (!ret) {
> >   			if (unlikely(busyloop_intr)) {
> >   				vhost_poll_queue(&vq->poll);
> >   			} else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> > @@ -897,8 +912,8 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
> >   			struct ubuf_info *ubuf;
> >   			ubuf = nvq->ubuf_info + nvq->upend_idx;
> > -			vq->heads[nvq->upend_idx].id = cpu_to_vhost32(vq, head);
> > -			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
> > +			nvq->bufs[nvq->upend_idx] = buf;
> > +			nvq->bufs[nvq->upend_idx].in_len = VHOST_DMA_IN_PROGRESS;
> >   			ubuf->callback = vhost_zerocopy_callback;
> >   			ubuf->ctx = nvq->ubufs;
> >   			ubuf->desc = nvq->upend_idx;
> > @@ -930,17 +945,19 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
> >   				nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
> >   					% UIO_MAXIOV;
> >   			}
> > -			vhost_discard_vq_desc(vq, 1);
> > +			vhost_discard_avail_bufs(vq, &buf, 1);
> >   			vhost_net_enable_vq(net, vq);
> >   			break;
> >   		}
> >   		if (err != len)
> >   			pr_debug("Truncated TX packet: "
> >   				 " len %d != %zd\n", err, len);
> > -		if (!zcopy_used)
> > -			vhost_add_used_and_signal(&net->dev, vq, head, 0);
> > -		else
> > +		if (!zcopy_used) {
> > +			vhost_put_used_buf(vq, &buf);
> > +			vhost_signal(&net->dev, vq);
> 
> 
> Do we need something like vhost_put_used_and_signal()?
> 
> Thanks
> 
> 
> > +		} else {
> >   			vhost_zerocopy_signal_used(net, vq);
> > +		}
> >   		vhost_net_tx_packet(net);
> >   	} while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
> >   }
> > @@ -1004,7 +1021,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> >   	int len = peek_head_len(rnvq, sk);
> >   	if (!len && rvq->busyloop_timeout) {
> > -		/* Flush batched heads first */
> > +		/* Flush batched bufs first */
> >   		vhost_net_signal_used(rnvq);
> >   		/* Both tx vq and rx socket were polled here */
> >   		vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, true);
> > @@ -1022,11 +1039,11 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> >    * @iovcount	- returned count of io vectors we fill
> >    * @log		- vhost log
> >    * @log_num	- log offset
> > - * @quota       - headcount quota, 1 for big buffer
> > - *	returns number of buffer heads allocated, negative on error
> > + * @quota       - bufcount quota, 1 for big buffer
> > + *	returns number of buffers allocated, negative on error
> >    */
> >   static int get_rx_bufs(struct vhost_virtqueue *vq,
> > -		       struct vring_used_elem *heads,
> > +		       struct vhost_buf *bufs,
> >   		       int datalen,
> >   		       unsigned *iovcount,
> >   		       struct vhost_log *log,
> > @@ -1035,30 +1052,24 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
> >   {
> >   	unsigned int out, in;
> >   	int seg = 0;
> > -	int headcount = 0;
> > -	unsigned d;
> > +	int bufcount = 0;
> >   	int r, nlogs = 0;
> >   	/* len is always initialized before use since we are always called with
> >   	 * datalen > 0.
> >   	 */
> >   	u32 uninitialized_var(len);
> > -	while (datalen > 0 && headcount < quota) {
> > +	while (datalen > 0 && bufcount < quota) {
> >   		if (unlikely(seg >= UIO_MAXIOV)) {
> >   			r = -ENOBUFS;
> >   			goto err;
> >   		}
> > -		r = vhost_get_vq_desc(vq, vq->iov + seg,
> > -				      ARRAY_SIZE(vq->iov) - seg, &out,
> > -				      &in, log, log_num);
> > -		if (unlikely(r < 0))
> > +		r = vhost_get_avail_buf(vq, bufs + bufcount, vq->iov + seg,
> > +					ARRAY_SIZE(vq->iov) - seg, &out,
> > +					&in, log, log_num);
> > +		if (unlikely(r <= 0))
> >   			goto err;
> > -		d = r;
> > -		if (d == vq->num) {
> > -			r = 0;
> > -			goto err;
> > -		}
> >   		if (unlikely(out || in <= 0)) {
> >   			vq_err(vq, "unexpected descriptor format for RX: "
> >   				"out %d, in %d\n", out, in);
> > @@ -1069,14 +1080,12 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
> >   			nlogs += *log_num;
> >   			log += *log_num;
> >   		}
> > -		heads[headcount].id = cpu_to_vhost32(vq, d);
> >   		len = iov_length(vq->iov + seg, in);
> > -		heads[headcount].len = cpu_to_vhost32(vq, len);
> >   		datalen -= len;
> > -		++headcount;
> > +		++bufcount;
> >   		seg += in;
> >   	}
> > -	heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
> > +	bufs[bufcount - 1].in_len = len + datalen;
> >   	*iovcount = seg;
> >   	if (unlikely(log))
> >   		*log_num = nlogs;
> > @@ -1086,9 +1095,9 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
> >   		r = UIO_MAXIOV + 1;
> >   		goto err;
> >   	}
> > -	return headcount;
> > +	return bufcount;
> >   err:
> > -	vhost_discard_vq_desc(vq, headcount);
> > +	vhost_discard_avail_bufs(vq, bufs, bufcount);
> >   	return r;
> >   }
> > @@ -1113,7 +1122,7 @@ static void handle_rx(struct vhost_net *net)
> >   	};
> >   	size_t total_len = 0;
> >   	int err, mergeable;
> > -	s16 headcount;
> > +	int bufcount;
> >   	size_t vhost_hlen, sock_hlen;
> >   	size_t vhost_len, sock_len;
> >   	bool busyloop_intr = false;
> > @@ -1147,14 +1156,14 @@ static void handle_rx(struct vhost_net *net)
> >   			break;
> >   		sock_len += sock_hlen;
> >   		vhost_len = sock_len + vhost_hlen;
> > -		headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
> > -					vhost_len, &in, vq_log, &log,
> > -					likely(mergeable) ? UIO_MAXIOV : 1);
> > +		bufcount = get_rx_bufs(vq, nvq->bufs + nvq->done_idx,
> > +				       vhost_len, &in, vq_log, &log,
> > +				       likely(mergeable) ? UIO_MAXIOV : 1);
> >   		/* On error, stop handling until the next kick. */
> > -		if (unlikely(headcount < 0))
> > +		if (unlikely(bufcount < 0))
> >   			goto out;
> >   		/* OK, now we need to know about added descriptors. */
> > -		if (!headcount) {
> > +		if (!bufcount) {
> >   			if (unlikely(busyloop_intr)) {
> >   				vhost_poll_queue(&vq->poll);
> >   			} else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> > @@ -1171,7 +1180,7 @@ static void handle_rx(struct vhost_net *net)
> >   		if (nvq->rx_ring)
> >   			msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
> >   		/* On overrun, truncate and discard */
> > -		if (unlikely(headcount > UIO_MAXIOV)) {
> > +		if (unlikely(bufcount > UIO_MAXIOV)) {
> >   			iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
> >   			err = sock->ops->recvmsg(sock, &msg,
> >   						 1, MSG_DONTWAIT | MSG_TRUNC);
> > @@ -1195,7 +1204,7 @@ static void handle_rx(struct vhost_net *net)
> >   		if (unlikely(err != sock_len)) {
> >   			pr_debug("Discarded rx packet: "
> >   				 " len %d, expected %zd\n", err, sock_len);
> > -			vhost_discard_vq_desc(vq, headcount);
> > +			vhost_discard_avail_bufs(vq, nvq->bufs + nvq->done_idx, bufcount);
> >   			continue;
> >   		}
> >   		/* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
> > @@ -1214,15 +1223,15 @@ static void handle_rx(struct vhost_net *net)
> >   		}
> >   		/* TODO: Should check and handle checksum. */
> > -		num_buffers = cpu_to_vhost16(vq, headcount);
> > +		num_buffers = cpu_to_vhost16(vq, bufcount);
> >   		if (likely(mergeable) &&
> >   		    copy_to_iter(&num_buffers, sizeof num_buffers,
> >   				 &fixup) != sizeof num_buffers) {
> >   			vq_err(vq, "Failed num_buffers write");
> > -			vhost_discard_vq_desc(vq, headcount);
> > +			vhost_discard_avail_bufs(vq, nvq->bufs + nvq->done_idx, bufcount);
> >   			goto out;
> >   		}
> > -		nvq->done_idx += headcount;
> > +		nvq->done_idx += bufcount;
> >   		if (nvq->done_idx > VHOST_NET_BATCH)
> >   			vhost_net_signal_used(nvq);
> >   		if (unlikely(vq_log))