Linux Virtualization - Jul 2014 - [PATCH RFC 1/2] virtio: support for urgent descriptors

Below should be useful for some experiments Jason is doing.
I thought I'd send it out for early review/feedback.

Compiled-only at this point.

event idx feature allows us to defer interrupts until
a specific # of descriptors were used.
Sometimes it might be useful to get an interrupt after
a specific descriptor, regardless.
This adds a descriptor flag for this, and an API
to create an urgent output descriptor.
This is still an RFC:
we'll need a feature bit for drivers to detect this,
but we've run out of feature bits for virtio 0.X.
For experimentation purposes, drivers can assume
this is set, or add a driver-specific feature bit.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio.h           |  6 ++++++
 include/uapi/linux/virtio_ring.h |  3 +++
 drivers/virtio/virtio_ring.c     | 46 ++++++++++++++++++++++++++++++++++++----
 3 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b46671e..14625a6 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -39,6 +39,12 @@ int virtqueue_add_outbuf(struct virtqueue *vq,
 			 void *data,
 			 gfp_t gfp);
 
+int virtqueue_add_outbuf_urgent(struct virtqueue *vq,
+				struct scatterlist sg[], unsigned int num,
+				void *data,
+				gfp_t gfp);
+
+
 int virtqueue_add_inbuf(struct virtqueue *vq,
 			struct scatterlist sg[], unsigned int num,
 			void *data,
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index a99f9b7..d08b1e6 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -39,6 +39,9 @@
 #define VRING_DESC_F_WRITE	2
 /* This means the buffer contains a list of buffer descriptors. */
 #define VRING_DESC_F_INDIRECT	4
+/* This means the descriptor should cause an interrupt
+ * ignoring avail event idx. */
+#define VRING_DESC_F_URGENT	8
 
 /* The Host uses this in used->flags to advise the Guest: don't kick me
when
  * you add a buffer.  It's unreliable, so it's simply an optimization. 
Guest
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 4d08f45a..3e448b9 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -115,6 +115,7 @@ static inline struct scatterlist *sg_next_arr(struct
scatterlist *sg,
 
 /* Set up an indirect table of descriptors and add it to the queue. */
 static inline int vring_add_indirect(struct vring_virtqueue *vq,
+				     bool urgent,
 				     struct scatterlist *sgs[],
 				     struct scatterlist *(*next)
 				       (struct scatterlist *, unsigned int *),
@@ -173,6 +174,8 @@ static inline int vring_add_indirect(struct vring_virtqueue
*vq,
 	/* Use a single buffer which doesn't continue */
 	head = vq->free_head;
 	vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
+	if (urgent)
+		vq->vring.desc[head].flags |= VRING_DESC_F_URGENT;
 	vq->vring.desc[head].addr = virt_to_phys(desc);
 	/* kmemleak gives a false positive, as it's hidden by virt_to_phys */
 	kmemleak_ignore(desc);
@@ -185,6 +188,7 @@ static inline int vring_add_indirect(struct vring_virtqueue
*vq,
 }
 
 static inline int virtqueue_add(struct virtqueue *_vq,
+			        bool urgent,
 				struct scatterlist *sgs[],
 				struct scatterlist *(*next)
 				  (struct scatterlist *, unsigned int *),
@@ -227,7 +231,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	/* If the host supports indirect descriptor tables, and we have multiple
 	 * buffers, then go indirect. FIXME: tune this threshold */
 	if (vq->indirect && total_sg > 1 && vq->vq.num_free)
{
-		head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
+		head = vring_add_indirect(vq, urgent, sgs, next, total_sg, total_out,
 					  total_in,
 					  out_sgs, in_sgs, gfp);
 		if (likely(head >= 0))
@@ -256,6 +260,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	for (n = 0; n < out_sgs; n++) {
 		for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
 			vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
+			if (urgent) {
+				vq->vring.desc[head].flags |= VRING_DESC_F_URGENT;
+				urgent = false;
+			}
 			vq->vring.desc[i].addr = sg_phys(sg);
 			vq->vring.desc[i].len = sg->length;
 			prev = i;
@@ -265,6 +273,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	for (; n < (out_sgs + in_sgs); n++) {
 		for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
 			vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
+			if (urgent) {
+				vq->vring.desc[head].flags |= VRING_DESC_F_URGENT;
+				urgent = false;
+			}
 			vq->vring.desc[i].addr = sg_phys(sg);
 			vq->vring.desc[i].len = sg->length;
 			prev = i;
@@ -305,6 +317,8 @@ add_head:
 
 /**
  * virtqueue_add_sgs - expose buffers to other end
+ * @urgent: in case virtqueue_enable_cb_delayed was called, cause an interrupt
+ *          after this descriptor was completed
  * @vq: the struct virtqueue we're talking about.
  * @sgs: array of terminated scatterlists.
  * @out_num: the number of scatterlists readable by other side
@@ -337,7 +351,7 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
 		for (sg = sgs[i]; sg; sg = sg_next(sg))
 			total_in++;
 	}
-	return virtqueue_add(_vq, sgs, sg_next_chained,
+	return virtqueue_add(_vq, false, sgs, sg_next_chained,
 			     total_out, total_in, out_sgs, in_sgs, data, gfp);
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
@@ -360,11 +374,35 @@ int virtqueue_add_outbuf(struct virtqueue *vq,
 			 void *data,
 			 gfp_t gfp)
 {
-	return virtqueue_add(vq, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
+	return virtqueue_add(vq, false, &sg, sg_next_arr, num, 0, 1, 0, data,
gfp);
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);
 
 /**
+ * virtqueue_add_outbuf - expose output buffers to other end
+ *          in case virtqueue_enable_cb_delayed was called, cause an interrupt
+ *          after this descriptor was completed
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of scatterlists (need not be terminated!)
+ * @num: the number of scatterlists readable by other side
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
+ */
+int virtqueue_add_outbuf_urgent(struct virtqueue *vq,
+			 struct scatterlist sg[], unsigned int num,
+			 void *data,
+			 gfp_t gfp)
+{
+	return virtqueue_add(vq, true, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_outbuf_urgent);
+
+/**
  * virtqueue_add_inbuf - expose input buffers to other end
  * @vq: the struct virtqueue we're talking about.
  * @sgs: array of scatterlists (need not be terminated!)
@@ -382,7 +420,7 @@ int virtqueue_add_inbuf(struct virtqueue *vq,
 			void *data,
 			gfp_t gfp)
 {
-	return virtqueue_add(vq, &sg, sg_next_arr, 0, num, 0, 1, data, gfp);
+	return virtqueue_add(vq, false, &sg, sg_next_arr, 0, num, 0, 1, data,
gfp);
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);
 
-- 
MST

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/vhost/vhost.h | 19 +++++++++++++------
 drivers/vhost/net.c   | 30 +++++++++++++++++++++---------
 drivers/vhost/scsi.c  | 23 +++++++++++++++--------
 drivers/vhost/test.c  |  5 +++--
 drivers/vhost/vhost.c | 23 ++++++++++++++++-------
 5 files changed, 68 insertions(+), 32 deletions(-)

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 3eda654..61ca542 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -96,6 +96,9 @@ struct vhost_virtqueue {
 	/* Last used index value we have signalled on */
 	bool signalled_used_valid;
 
+	/* Urgent descriptor was used */
+	bool urgent;
+
 	/* Log writes to used structure. */
 	bool log_used;
 	u64 log_addr;
@@ -138,20 +141,24 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl,
void __user *argp);
 int vhost_vq_access_ok(struct vhost_virtqueue *vq);
 int vhost_log_access_ok(struct vhost_dev *);
 
-int vhost_get_vq_desc(struct vhost_virtqueue *,
+int vhost_get_vq_desc(struct vhost_virtqueue *, bool *urgent,
 		      struct iovec iov[], unsigned int iov_count,
 		      unsigned int *out_num, unsigned int *in_num,
 		      struct vhost_log *log, unsigned int *log_num);
 void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
 
 int vhost_init_used(struct vhost_virtqueue *);
-int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
-int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
-		     unsigned count);
-void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
+int vhost_add_used(struct vhost_virtqueue *, bool urgent,
+		   unsigned int head, int len);
+int vhost_add_used_n(struct vhost_virtqueue *, bool urgent,
+		     struct vring_used_elem *heads, unsigned count);
+void vhost_add_used_and_signal(struct vhost_dev *,
+			       struct vhost_virtqueue *,
+			       bool urgent,
 			       unsigned int id, int len);
 void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
-			       struct vring_used_elem *heads, unsigned count);
+				 bool urgent,
+				 struct vring_used_elem *heads, unsigned count);
 void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
 void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8dae2f7..5f0567f 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -48,9 +48,11 @@ 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	3
+#define VHOST_DMA_FAILED_LEN	4
 /* Lower device DMA done */
-#define VHOST_DMA_DONE_LEN	2
+#define VHOST_DMA_DONE_LEN	3
+/* Lower device DMA in progress, urgent bit set */
+#define VHOST_DMA_URGENT	2
 /* Lower device DMA in progress */
 #define VHOST_DMA_IN_PROGRESS	1
 /* Buffer unused */
@@ -284,11 +286,13 @@ static void vhost_zerocopy_signal_used(struct vhost_net
*net,
 		container_of(vq, struct vhost_net_virtqueue, vq);
 	int i, add;
 	int j = 0;
+	bool urgent = false;
 
 	for (i = nvq->done_idx; i != nvq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
 		if (vq->heads[i].len == VHOST_DMA_FAILED_LEN)
 			vhost_net_tx_err(net);
 		if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
+			urgent = urgent || vq->heads[i].len == VHOST_DMA_URGENT;
 			vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
 			++j;
 		} else
@@ -296,7 +300,7 @@ static void vhost_zerocopy_signal_used(struct vhost_net
*net,
 	}
 	while (j) {
 		add = min(UIO_MAXIOV - nvq->done_idx, j);
-		vhost_add_used_and_signal_n(vq->dev, vq,
+		vhost_add_used_and_signal_n(vq->dev, vq, urgent,
 					    &vq->heads[nvq->done_idx], add);
 		nvq->done_idx = (nvq->done_idx + add) % UIO_MAXIOV;
 		j -= add;
@@ -363,6 +367,7 @@ static void handle_tx(struct vhost_net *net)
 	zcopy = nvq->ubufs;
 
 	for (;;) {
+		bool urgent;
 		/* Release DMAs done buffers first */
 		if (zcopy)
 			vhost_zerocopy_signal_used(net, vq);
@@ -374,7 +379,7 @@ static void handle_tx(struct vhost_net *net)
 			      % UIO_MAXIOV == nvq->done_idx))
 			break;
 
-		head = vhost_get_vq_desc(vq, vq->iov,
+		head = vhost_get_vq_desc(vq, &urgent, vq->iov,
 					 ARRAY_SIZE(vq->iov),
 					 &out, &in,
 					 NULL, NULL);
@@ -417,7 +422,8 @@ static void handle_tx(struct vhost_net *net)
 			ubuf = nvq->ubuf_info + nvq->upend_idx;
 
 			vq->heads[nvq->upend_idx].id = head;
-			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
+			vq->heads[nvq->upend_idx].len = urgent ?
+				VHOST_DMA_IN_PROGRESS : VHOST_DMA_URGENT;
 			ubuf->callback = vhost_zerocopy_callback;
 			ubuf->ctx = nvq->ubufs;
 			ubuf->desc = nvq->upend_idx;
@@ -445,7 +451,7 @@ static void handle_tx(struct vhost_net *net)
 			pr_debug("Truncated TX packet: "
 				 " len %d != %zd\n", err, len);
 		if (!zcopy_used)
-			vhost_add_used_and_signal(&net->dev, vq, head, 0);
+			vhost_add_used_and_signal(&net->dev, vq, urgent, head, 0);
 		else
 			vhost_zerocopy_signal_used(net, vq);
 		total_len += len;
@@ -488,6 +494,7 @@ static int peek_head_len(struct sock *sk)
  *	returns number of buffer heads allocated, negative on error
  */
 static int get_rx_bufs(struct vhost_virtqueue *vq,
+		       bool *urgentp,
 		       struct vring_used_elem *heads,
 		       int datalen,
 		       unsigned *iovcount,
@@ -502,11 +509,13 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 	int r, nlogs = 0;
 
 	while (datalen > 0 && headcount < quota) {
+		bool urgent;
+
 		if (unlikely(seg >= UIO_MAXIOV)) {
 			r = -ENOBUFS;
 			goto err;
 		}
-		r = vhost_get_vq_desc(vq, vq->iov + seg,
+		r = vhost_get_vq_desc(vq, &urgent, vq->iov + seg,
 				      ARRAY_SIZE(vq->iov) - seg, &out,
 				      &in, log, log_num);
 		if (unlikely(r < 0))
@@ -527,6 +536,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 			nlogs += *log_num;
 			log += *log_num;
 		}
+		*urgentp = *urgentp || urgent;
 		heads[headcount].id = d;
 		heads[headcount].len = iov_length(vq->iov + seg, in);
 		datalen -= heads[headcount].len;
@@ -590,9 +600,11 @@ static void handle_rx(struct vhost_net *net)
 	mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
 
 	while ((sock_len = peek_head_len(sock->sk))) {
+		bool urgent;
+
 		sock_len += sock_hlen;
 		vhost_len = sock_len + vhost_hlen;
-		headcount = get_rx_bufs(vq, vq->heads, vhost_len,
+		headcount = get_rx_bufs(vq, &urgent, vq->heads, vhost_len,
 					&in, vq_log, &log,
 					likely(mergeable) ? UIO_MAXIOV : 1);
 		/* On error, stop handling until the next kick. */
@@ -654,7 +666,7 @@ static void handle_rx(struct vhost_net *net)
 			vhost_discard_vq_desc(vq, headcount);
 			break;
 		}
-		vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
+		vhost_add_used_and_signal_n(&net->dev, vq, urgent, vq->heads,
 					    headcount);
 		if (unlikely(vq_log))
 			vhost_log_write(vq, vq_log, log, vhost_len);
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 69906ca..0a7e5bc 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -72,6 +72,8 @@ struct tcm_vhost_cmd {
 	int tvc_vq_desc;
 	/* virtio-scsi initiator task attribute */
 	int tvc_task_attr;
+	/* Descriptor urgent? */
+	bool tvc_vq_desc_urgent;
 	/* virtio-scsi initiator data direction */
 	enum dma_data_direction tvc_data_direction;
 	/* Expected data transfer length from virtio-scsi header */
@@ -606,6 +608,7 @@ tcm_vhost_do_evt_work(struct vhost_scsi *vs, struct
tcm_vhost_evt *evt)
 	struct virtio_scsi_event __user *eventp;
 	unsigned out, in;
 	int head, ret;
+	bool urgent;
 
 	if (!vq->private_data) {
 		vs->vs_events_missed = true;
@@ -614,7 +617,7 @@ tcm_vhost_do_evt_work(struct vhost_scsi *vs, struct
tcm_vhost_evt *evt)
 
 again:
 	vhost_disable_notify(&vs->dev, vq);
-	head = vhost_get_vq_desc(vq, vq->iov,
+	head = vhost_get_vq_desc(vq, &urgent, vq->iov,
 			ARRAY_SIZE(vq->iov), &out, &in,
 			NULL, NULL);
 	if (head < 0) {
@@ -643,7 +646,7 @@ again:
 	eventp = vq->iov[out].iov_base;
 	ret = __copy_to_user(eventp, event, sizeof(*event));
 	if (!ret)
-		vhost_add_used_and_signal(&vs->dev, vq, head, 0);
+		vhost_add_used_and_signal(&vs->dev, vq, urgent, head, 0);
 	else
 		vq_err(vq, "Faulted on tcm_vhost_send_event\n");
 }
@@ -704,7 +707,8 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work
*work)
 		ret = copy_to_user(cmd->tvc_resp, &v_rsp, sizeof(v_rsp));
 		if (likely(ret == 0)) {
 			struct vhost_scsi_virtqueue *q;
-			vhost_add_used(cmd->tvc_vq, cmd->tvc_vq_desc, 0);
+			vhost_add_used(cmd->tvc_vq, cmd->tvc_vq_desc_urgent,
+				       cmd->tvc_vq_desc, 0);
 			q = container_of(cmd->tvc_vq, struct vhost_scsi_virtqueue, vq);
 			vq = q - vs->vqs;
 			__set_bit(vq, signal);
@@ -947,6 +951,7 @@ static void tcm_vhost_submission_work(struct work_struct
*work)
 static void
 vhost_scsi_send_bad_target(struct vhost_scsi *vs,
 			   struct vhost_virtqueue *vq,
+			   bool urgent,
 			   int head, unsigned out)
 {
 	struct virtio_scsi_cmd_resp __user *resp;
@@ -958,7 +963,7 @@ vhost_scsi_send_bad_target(struct vhost_scsi *vs,
 	resp = vq->iov[out].iov_base;
 	ret = __copy_to_user(resp, &rsp, sizeof(rsp));
 	if (!ret)
-		vhost_add_used_and_signal(&vs->dev, vq, head, 0);
+		vhost_add_used_and_signal(&vs->dev, vq, urgent, head, 0);
 	else
 		pr_err("Faulted on virtio_scsi_cmd_resp\n");
 }
@@ -980,6 +985,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct
vhost_virtqueue *vq)
 	u8 *target, *lunp, task_attr;
 	bool hdr_pi;
 	void *req, *cdb;
+	bool urgent;
 
 	mutex_lock(&vq->mutex);
 	/*
@@ -993,7 +999,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct
vhost_virtqueue *vq)
 	vhost_disable_notify(&vs->dev, vq);
 
 	for (;;) {
-		head = vhost_get_vq_desc(vq, vq->iov,
+		head = vhost_get_vq_desc(vq, &urgent, vq->iov,
 					ARRAY_SIZE(vq->iov), &out, &in,
 					NULL, NULL);
 		pr_debug("vhost_get_vq_desc: head: %d, out: %u in: %u\n",
@@ -1067,7 +1073,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct
vhost_virtqueue *vq)
 
 		/* virtio-scsi spec requires byte 0 of the lun to be 1 */
 		if (unlikely(*lunp != 1)) {
-			vhost_scsi_send_bad_target(vs, vq, head, out);
+			vhost_scsi_send_bad_target(vs, vq, urgent, head, out);
 			continue;
 		}
 
@@ -1075,7 +1081,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct
vhost_virtqueue *vq)
 
 		/* Target does not exist, fail the request */
 		if (unlikely(!tpg)) {
-			vhost_scsi_send_bad_target(vs, vq, head, out);
+			vhost_scsi_send_bad_target(vs, vq, urgent, head, out);
 			continue;
 		}
 
@@ -1187,6 +1193,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct
vhost_virtqueue *vq)
 		 * tcm_vhost_queue_data_in() and tcm_vhost_queue_status()
 		 */
 		cmd->tvc_vq_desc = head;
+		cmd->tvc_vq_desc_urgent = urgent;
 		/*
 		 * Dispatch tv_cmd descriptor for cmwq execution in process
 		 * context provided by tcm_vhost_workqueue.  This also ensures
@@ -1203,7 +1210,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct
vhost_virtqueue *vq)
 err_free:
 	vhost_scsi_free_cmd(cmd);
 err_cmd:
-	vhost_scsi_send_bad_target(vs, vq, head, out);
+	vhost_scsi_send_bad_target(vs, vq, urgent, head, out);
 out:
 	mutex_unlock(&vq->mutex);
 }
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index d9c501e..757f3a2 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -42,6 +42,7 @@ static void handle_vq(struct vhost_test *n)
 	int head;
 	size_t len, total_len = 0;
 	void *private;
+	bool urgent;
 
 	mutex_lock(&vq->mutex);
 	private = vq->private_data;
@@ -53,7 +54,7 @@ static void handle_vq(struct vhost_test *n)
 	vhost_disable_notify(&n->dev, vq);
 
 	for (;;) {
-		head = vhost_get_vq_desc(vq, vq->iov,
+		head = vhost_get_vq_desc(vq, &urgent, vq->iov,
 					 ARRAY_SIZE(vq->iov),
 					 &out, &in,
 					 NULL, NULL);
@@ -79,7 +80,7 @@ static void handle_vq(struct vhost_test *n)
 			vq_err(vq, "Unexpected 0 len for TX\n");
 			break;
 		}
-		vhost_add_used_and_signal(&n->dev, vq, head, 0);
+		vhost_add_used_and_signal(&n->dev, vq, urgent,  head, 0);
 		total_len += len;
 		if (unlikely(total_len >= VHOST_TEST_WEIGHT)) {
 			vhost_poll_queue(&vq->poll);
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c90f437..0dcd9d2 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -186,6 +186,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->last_used_idx = 0;
 	vq->signalled_used = 0;
 	vq->signalled_used_valid = false;
+	vq->urgent = false;
 	vq->used_flags = 0;
 	vq->log_used = false;
 	vq->log_addr = -1ull;
@@ -1201,7 +1202,7 @@ static int get_indirect(struct vhost_virtqueue *vq,
  * This function returns the descriptor number found, or vq->num (which is
  * never a valid descriptor number) if none was found.  A negative code is
  * returned on error. */
-int vhost_get_vq_desc(struct vhost_virtqueue *vq,
+int vhost_get_vq_desc(struct vhost_virtqueue *vq, bool *urgent,
 		      struct iovec iov[], unsigned int iov_size,
 		      unsigned int *out_num, unsigned int *in_num,
 		      struct vhost_log *log, unsigned int *log_num)
@@ -1251,6 +1252,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 
 	/* When we start there are none of either input nor output. */
 	*out_num = *in_num = 0;
+	*urgent = false;
 	if (unlikely(log))
 		*log_num = 0;
 
@@ -1274,6 +1276,8 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 			       i, vq->desc + i);
 			return -EFAULT;
 		}
+		if (desc.flags & VRING_DESC_F_URGENT)
+			*urgent = true;
 		if (desc.flags & VRING_DESC_F_INDIRECT) {
 			ret = get_indirect(vq, iov, iov_size,
 					   out_num, in_num,
@@ -1333,11 +1337,11 @@ EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);
 
 /* After we've used one of their buffers, we tell them about it.  We'll
then
  * want to notify the guest, using eventfd. */
-int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
+int vhost_add_used(struct vhost_virtqueue *vq, bool urgent, unsigned int head,
int len)
 {
 	struct vring_used_elem heads = { head, len };
 
-	return vhost_add_used_n(vq, &heads, 1);
+	return vhost_add_used_n(vq, urgent, &heads, 1);
 }
 EXPORT_SYMBOL_GPL(vhost_add_used);
 
@@ -1386,7 +1390,8 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 
 /* After we've used one of their buffers, we tell them about it.  We'll
then
  * want to notify the guest, using eventfd. */
-int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
+int vhost_add_used_n(struct vhost_virtqueue *vq, bool urgent,
+		     struct vring_used_elem *heads,
 		     unsigned count)
 {
 	int start, n, r;
@@ -1416,6 +1421,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct
vring_used_elem *heads,
 		if (vq->log_ctx)
 			eventfd_signal(vq->log_ctx, 1);
 	}
+	vq->urgent = vq->urgent || urgent;
 	return r;
 }
 EXPORT_SYMBOL_GPL(vhost_add_used_n);
@@ -1433,12 +1439,13 @@ static bool vhost_notify(struct vhost_dev *dev, struct
vhost_virtqueue *vq)
 	    unlikely(vq->avail_idx == vq->last_avail_idx))
 		return true;
 
-	if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
+	if (vq->urgent || !vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
 		__u16 flags;
 		if (__get_user(flags, &vq->avail->flags)) {
 			vq_err(vq, "Failed to get flags");
 			return true;
 		}
+		vq->urgent = false;
 		return !(flags & VRING_AVAIL_F_NO_INTERRUPT);
 	}
 	old = vq->signalled_used;
@@ -1468,9 +1475,10 @@ EXPORT_SYMBOL_GPL(vhost_signal);
 /* And here's the combo meal deal.  Supersize me! */
 void vhost_add_used_and_signal(struct vhost_dev *dev,
 			       struct vhost_virtqueue *vq,
+			       bool urgent,
 			       unsigned int head, int len)
 {
-	vhost_add_used(vq, head, len);
+	vhost_add_used(vq, urgent, head, len);
 	vhost_signal(dev, vq);
 }
 EXPORT_SYMBOL_GPL(vhost_add_used_and_signal);
@@ -1478,9 +1486,10 @@ EXPORT_SYMBOL_GPL(vhost_add_used_and_signal);
 /* multi-buffer version of vhost_add_used_and_signal */
 void vhost_add_used_and_signal_n(struct vhost_dev *dev,
 				 struct vhost_virtqueue *vq,
+				 bool urgent,
 				 struct vring_used_elem *heads, unsigned count)
 {
-	vhost_add_used_n(vq, heads, count);
+	vhost_add_used_n(vq, urgent, heads, count);
 	vhost_signal(dev, vq);
 }
 EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
-- 
MST

"Michael S. Tsirkin" <mst at redhat.com>
writes:
> Below should be useful for some experiments Jason is doing.
> I thought I'd send it out for early review/feedback.
>
> Compiled-only at this point.
It's not a terrible idea, but it will come down to how effective it is
in practice.

I'm tempted to make it v1.0 only though.

Cheers,
Rusty.

On 07/01/2014 06:49 PM, Michael S. Tsirkin wrote:
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/vhost/vhost.h | 19 +++++++++++++------
>  drivers/vhost/net.c   | 30 +++++++++++++++++++++---------
>  drivers/vhost/scsi.c  | 23 +++++++++++++++--------
>  drivers/vhost/test.c  |  5 +++--
>  drivers/vhost/vhost.c | 23 ++++++++++++++++-------
>  5 files changed, 68 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 3eda654..61ca542 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
[...]
>  EXPORT_SYMBOL_GPL(vhost_add_used_n);
> @@ -1433,12 +1439,13 @@ static bool vhost_notify(struct vhost_dev *dev,
struct vhost_virtqueue *vq)
>  	    unlikely(vq->avail_idx == vq->last_avail_idx))
>  		return true;
>  
> -	if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
> +	if (vq->urgent || !vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
So the urgent descriptor only work when event index was not enabled?
This seems suboptimal, we may still want to benefit from event index
even if urgent descriptor is used. Looks like we need return true here
when vq->urgent is true?

Another question is whether or not we need to do this a new flag.
Technically we can do it purely in guest side through event index, this
can help to eliminate both the changes in host and a new feature
bit.
>  		__u16 flags;
>  		if (__get_user(flags, &vq->avail->flags)) {
>  			vq_err(vq, "Failed to get flags");
>  			return true;
>  		}
> +		vq->urgent = false;
>  		return !(flags & VRING_AVAIL_F_NO_INTERRUPT);
>  	}
>  	old = vq->signalled_used;
> @@ -1468,9 +1475,10 @@ EXPORT_SYMBOL_GPL(vhost_signal);
>  /* And here's the combo meal deal.  Supersize me! */
>  void vhost_add_used_and_signal(struct vhost_dev *dev,
>  			       struct vhost_virtqueue *vq,
> +			       bool urgent,
>  			       unsigned int head, int len)
>  {
> -	vhost_add_used(vq, head, len);
> +	vhost_add_used(vq, urgent, head, len);
>  	vhost_signal(dev, vq);
>  }
>  EXPORT_SYMBOL_GPL(vhost_add_used_and_signal);
> @@ -1478,9 +1486,10 @@ EXPORT_SYMBOL_GPL(vhost_add_used_and_signal);
>  /* multi-buffer version of vhost_add_used_and_signal */
>  void vhost_add_used_and_signal_n(struct vhost_dev *dev,
>  				 struct vhost_virtqueue *vq,
> +				 bool urgent,
>  				 struct vring_used_elem *heads, unsigned count)
>  {
> -	vhost_add_used_n(vq, heads, count);
> +	vhost_add_used_n(vq, urgent, heads, count);
>  	vhost_signal(dev, vq);
>  }
>  EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);

On 07/01/2014 06:49 PM, Michael S. Tsirkin wrote:
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/vhost/vhost.h | 19 +++++++++++++------
>  drivers/vhost/net.c   | 30 +++++++++++++++++++++---------
>  drivers/vhost/scsi.c  | 23 +++++++++++++++--------
>  drivers/vhost/test.c  |  5 +++--
>  drivers/vhost/vhost.c | 23 ++++++++++++++++-------
>  5 files changed, 68 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 3eda654..61ca542 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -96,6 +96,9 @@ struct vhost_virtqueue {
>  	/* Last used index value we have signalled on */
>  	bool signalled_used_valid;
>  
> +	/* Urgent descriptor was used */
> +	bool urgent;
> +
>  	/* Log writes to used structure. */
>  	bool log_used;
>  	u64 log_addr;
> @@ -138,20 +141,24 @@ long vhost_vring_ioctl(struct vhost_dev *d, int
ioctl, void __user *argp);
>  int vhost_vq_access_ok(struct vhost_virtqueue *vq);
>  int vhost_log_access_ok(struct vhost_dev *);
>  
> -int vhost_get_vq_desc(struct vhost_virtqueue *,
> +int vhost_get_vq_desc(struct vhost_virtqueue *, bool *urgent,
>  		      struct iovec iov[], unsigned int iov_count,
>  		      unsigned int *out_num, unsigned int *in_num,
>  		      struct vhost_log *log, unsigned int *log_num);
>  void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
>  
>  int vhost_init_used(struct vhost_virtqueue *);
> -int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
> -int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem
*heads,
> -		     unsigned count);
> -void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue
*,
> +int vhost_add_used(struct vhost_virtqueue *, bool urgent,
> +		   unsigned int head, int len);
> +int vhost_add_used_n(struct vhost_virtqueue *, bool urgent,
> +		     struct vring_used_elem *heads, unsigned count);
> +void vhost_add_used_and_signal(struct vhost_dev *,
> +			       struct vhost_virtqueue *,
> +			       bool urgent,
>  			       unsigned int id, int len);
>  void vhost_add_used_and_signal_n(struct vhost_dev *, struct
vhost_virtqueue *,
> -			       struct vring_used_elem *heads, unsigned count);
> +				 bool urgent,
> +				 struct vring_used_elem *heads, unsigned count);
>  void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
>  void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
>  bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 8dae2f7..5f0567f 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -48,9 +48,11 @@ 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	3
> +#define VHOST_DMA_FAILED_LEN	4
>  /* Lower device DMA done */
> -#define VHOST_DMA_DONE_LEN	2
> +#define VHOST_DMA_DONE_LEN	3
> +/* Lower device DMA in progress, urgent bit set */
> +#define VHOST_DMA_URGENT	2
>  /* Lower device DMA in progress */
>  #define VHOST_DMA_IN_PROGRESS	1
>  /* Buffer unused */
> @@ -284,11 +286,13 @@ static void vhost_zerocopy_signal_used(struct
vhost_net *net,
>  		container_of(vq, struct vhost_net_virtqueue, vq);
>  	int i, add;
>  	int j = 0;
> +	bool urgent = false;
>  
>  	for (i = nvq->done_idx; i != nvq->upend_idx; i = (i + 1) %
UIO_MAXIOV) {
>  		if (vq->heads[i].len == VHOST_DMA_FAILED_LEN)
>  			vhost_net_tx_err(net);
>  		if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
> +			urgent = urgent || vq->heads[i].len == VHOST_DMA_URGENT;
A problem is len was either VHOST_DMA_DONE_LEN or VHOST_DMA_FAILED_LEN
here. Looks like we need another new VHOST_DMA_DONE_LEN_URGENT and
change the len to this value if it was an urgent descriptor in zerocopy
callback.
>  			vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
>  			++j;
>  		} else
> @@ -296,7 +300,7 @@ static void vhost_zerocopy_signal_used(struct vhost_net
*net,
>  	}
>  	while (j) {
>  		add = min(UIO_MAXIOV - nvq->done_idx, j);
> -		vhost_add_used_and_signal_n(vq->dev, vq,
> +		vhost_add_used_and_signal_n(vq->dev, vq, urgent,
>  					    &vq->heads[nvq->done_idx], add);
>  		nvq->done_idx = (nvq->done_idx + add) % UIO_MAXIOV;
>  		j -= add;
> @@ -363,6 +367,7 @@ static void handle_tx(struct vhost_net *net)
>  	zcopy = nvq->ubufs;
>  
>  	for (;;) {
> +		bool urgent;
>  		/* Release DMAs done buffers first */
>  		if (zcopy)
>  			vhost_zerocopy_signal_used(net, vq);
> @@ -374,7 +379,7 @@ static void handle_tx(struct vhost_net *net)
>  			      % UIO_MAXIOV == nvq->done_idx))
>  			break;
>  
> -		head = vhost_get_vq_desc(vq, vq->iov,
> +		head = vhost_get_vq_desc(vq, &urgent, vq->iov,
>  					 ARRAY_SIZE(vq->iov),
>  					 &out, &in,
>  					 NULL, NULL);
> @@ -417,7 +422,8 @@ static void handle_tx(struct vhost_net *net)
>  			ubuf = nvq->ubuf_info + nvq->upend_idx;
>  
>  			vq->heads[nvq->upend_idx].id = head;
> -			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
> +			vq->heads[nvq->upend_idx].len = urgent ?
> +				VHOST_DMA_IN_PROGRESS : VHOST_DMA_URGENT;
I think you mean VHOST_DMA_URGENT : VHOST_DMA_IN_PROGRESS here.

With all the changes above, zercopy mode works as expected. I will post
the driver part code and result next week for early review.

Thanks
>  			ubuf->callback = vhost_zerocopy_callback;
>  			ubuf->ctx = nvq->ubufs;
>  			ubuf->desc = nvq->upend_idx;
> @@ -445,7 +451,7 @@ static void handle_tx(struct vhost_net *net)
>  			pr_debug("Truncated TX packet: "
>  				 " len %d != %zd\n", err, len);
>  		if (!zcopy_used)
> -			vhost_add_used_and_signal(&net->dev, vq, head, 0);
> +			vhost_add_used_and_signal(&net->dev, vq, urgent, head, 0);
>  		else
>  			vhost_zerocopy_signal_used(net, vq);
>  		total_len += len;
[...]

On Wed, Jul 09, 2014 at 09:58:43AM +0930, Rusty Russell
wrote:
> "Michael S. Tsirkin" <mst at redhat.com> writes:
> > Below should be useful for some experiments Jason is doing.
> > I thought I'd send it out for early review/feedback.
> >
> > Compiled-only at this point.
> 
> It's not a terrible idea, but it will come down to how effective it is
> in practice.
> 
> I'm tempted to make it v1.0 only though.
> 
> Cheers,
> Rusty.
Me too.