virtio: add support for tx-queue-size

Type: improvement

DBGvpp# set loggin class virtio level debug
DBGvpp# create int virtio 0000:00:03.0 tx-queue-size 1024

show virtio pci
```
  Virtqueue (TX) 1
    qsz 1024, last_used_idx 0, desc_next 0, desc_in_use 0
    avail.flags 0x1 avail.idx 0 used.flags 0x0 used.idx 0
```

show logging
```
2022/07/22 23:20:22:557 debug      virtio         0000:00:03.0: tx-queue: number 1, default-size 256
2022/07/22 23:20:22:557 debug      virtio         0000:00:03.0: tx-queue: number 1, new size 1024
```

Change-Id: Ib1a3ebe742b3a6c9fe72bd1c5accfe07682cbdd1
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>

5 files changed, 27 insertions, 10 deletions

diff --git a/src/vnet/devices/virtio/FEATURE.yaml b/src/vnet/devices/virtio/FEATURE.yaml
index 5f4de207acd..446a45b61a3 100644
--- a/src/vnet/devices/virtio/FEATURE.yaml
+++ b/src/vnet/devices/virtio/FEATURE.yaml
@@ -11,6 +11,8 @@ features:
   - Support multi-queue, GSO, checksum offload, indirect descriptor,
     jumbo frame, and packed ring.
   - Support virtio 1.1 packed ring in vhost
+  - Support for tx queue size configuration (tested on host kernel 5.15
+    and qemu version 6.2.0)
 description: "Virtio implementation"
 missing:
   - API dump filtering by sw_if_index
diff --git a/src/vnet/devices/virtio/cli.c b/src/vnet/devices/virtio/cli.c
index 2457e9b686e..cadfd67df41 100644
--- a/src/vnet/devices/virtio/cli.c
+++ b/src/vnet/devices/virtio/cli.c
@@ -31,6 +31,7 @@ virtio_pci_create_command_fn (vlib_main_t * vm, unformat_input_t * input,
   virtio_pci_create_if_args_t args;
   u64 feature_mask = (u64) ~ (0ULL);
   u32 buffering_size = 0;
+  u32 txq_size = 0;
 
   /* Get a line of input. */
   if (!unformat_user (input, unformat_line_input, line_input))
@@ -43,6 +44,8 @@ virtio_pci_create_command_fn (vlib_main_t * vm, unformat_input_t * input,
 	;
       else if (unformat (line_input, "feature-mask 0x%llx", &feature_mask))
 	args.features = feature_mask;
+      if (unformat (line_input, "tx-queue-size %u", &txq_size))
+	args.tx_queue_size = txq_size;
       else if (unformat (line_input, "gso-enabled"))
 	args.gso_enabled = 1;
       else if (unformat (line_input, "csum-enabled"))
@@ -74,7 +77,8 @@ virtio_pci_create_command_fn (vlib_main_t * vm, unformat_input_t * input,
 VLIB_CLI_COMMAND (virtio_pci_create_command, static) = {
   .path = "create interface virtio",
   .short_help = "create interface virtio <pci-address> "
-		"[feature-mask <hex-mask>] [gso-enabled] [csum-enabled] "
+		"[feature-mask <hex-mask>] [tx-queue-size <size>] "
+		"[gso-enabled] [csum-enabled] "
 		"[buffering [size <buffering-szie>]] [packed] [bind [force]]",
   .function = virtio_pci_create_command_fn,
 };
diff --git a/src/vnet/devices/virtio/pci.c b/src/vnet/devices/virtio/pci.c
index 85e6abdbbe5..0820f8a5016 100644
--- a/src/vnet/devices/virtio/pci.c
+++ b/src/vnet/devices/virtio/pci.c
@@ -721,8 +721,8 @@ virtio_pci_control_vring_init (vlib_main_t * vm, virtio_if_t * vif,
 }
 
 clib_error_t *
-virtio_pci_vring_split_init (vlib_main_t * vm, virtio_if_t * vif,
-			     u16 queue_num)
+virtio_pci_vring_split_init (vlib_main_t *vm, virtio_if_t *vif, u16 queue_num,
+			     u16 txq_size)
 {
   clib_error_t *error = 0;
   u16 queue_size = 0;
@@ -745,6 +745,16 @@ virtio_pci_vring_split_init (vlib_main_t * vm, virtio_if_t * vif,
 
   if (queue_num % 2)
     {
+      if (txq_size)
+	{
+	  virtio_log_debug (vif, "tx-queue: number %u, default-size %u",
+			    queue_num, queue_size);
+	  vif->virtio_pci_func->set_queue_size (vm, vif, queue_num, txq_size);
+	  queue_size =
+	    vif->virtio_pci_func->get_queue_size (vm, vif, queue_num);
+	  virtio_log_debug (vif, "tx-queue: number %u, new size %u", queue_num,
+			    queue_size);
+	}
       vec_validate_aligned (vif->txq_vrings, TX_QUEUE_ACCESS (queue_num),
 			    CLIB_CACHE_LINE_BYTES);
       vring = vec_elt_at_index (vif->txq_vrings, TX_QUEUE_ACCESS (queue_num));
@@ -886,12 +896,13 @@ virtio_pci_vring_packed_init (vlib_main_t * vm, virtio_if_t * vif,
 }
 
 clib_error_t *
-virtio_pci_vring_init (vlib_main_t * vm, virtio_if_t * vif, u16 queue_num)
+virtio_pci_vring_init (vlib_main_t *vm, virtio_if_t *vif, u16 queue_num,
+		       u16 txq_size)
 {
   if (vif->is_packed)
     return virtio_pci_vring_packed_init (vm, vif, queue_num);
   else
-    return virtio_pci_vring_split_init (vm, vif, queue_num);
+    return virtio_pci_vring_split_init (vm, vif, queue_num, txq_size);
 }
 
 static void
@@ -1229,7 +1240,7 @@ virtio_pci_device_init (vlib_main_t * vm, virtio_if_t * vif,
 
   for (int i = 0; i < vif->max_queue_pairs; i++)
     {
-      if ((error = virtio_pci_vring_init (vm, vif, RX_QUEUE (i))))
+      if ((error = virtio_pci_vring_init (vm, vif, RX_QUEUE (i), 0)))
 	{
 	  args->rv = VNET_API_ERROR_INIT_FAILED;
 	  virtio_log_error (vif, "%s (%u) %s", "error in rxq-queue",
@@ -1244,7 +1255,8 @@ virtio_pci_device_init (vlib_main_t * vm, virtio_if_t * vif,
 	  vif->num_rxqs++;
 	}
 
-      if ((error = virtio_pci_vring_init (vm, vif, TX_QUEUE (i))))
+      if ((error = virtio_pci_vring_init (vm, vif, TX_QUEUE (i),
+					  args->tx_queue_size)))
 	{
 	  args->rv = VNET_API_ERROR_INIT_FAILED;
 	  virtio_log_error (vif, "%s (%u) %s", "error in txq-queue",
diff --git a/src/vnet/devices/virtio/pci.h b/src/vnet/devices/virtio/pci.h
index 0cada61d9b8..2b23377999f 100644
--- a/src/vnet/devices/virtio/pci.h
+++ b/src/vnet/devices/virtio/pci.h
@@ -245,6 +245,7 @@ typedef struct
   u64 features;
   u8 gso_enabled;
   u8 checksum_offload_enabled;
+  u32 tx_queue_size;
   virtio_bind_t bind;
   u32 buffering_size;
   u32 virtio_flags;
diff --git a/src/vnet/devices/virtio/virtio_pci_modern.c b/src/vnet/devices/virtio/virtio_pci_modern.c
index f7313d84bbd..50a7b392367 100644
--- a/src/vnet/devices/virtio/virtio_pci_modern.c
+++ b/src/vnet/devices/virtio/virtio_pci_modern.c
@@ -164,9 +164,7 @@ virtio_pci_modern_set_queue_size (vlib_main_t * vm, virtio_if_t * vif,
       return;
     }
 
-  if (virtio_pci_modern_get_queue_size (vm, vif, queue_id) > queue_size)
-    virtio_pci_reg_write_u16 (vif, VIRTIO_QUEUE_SIZE_OFFSET (vif),
-			      queue_size);
+  virtio_pci_reg_write_u16 (vif, VIRTIO_QUEUE_SIZE_OFFSET (vif), queue_size);
 }
 
 static u16