[PATCH net-next 3/3] tun: introduce cpu id based steering policy

[Jason Wang]

This patch introduces a simple queue selection policy which just
choose txq based on processor id. This maybe useful for connectless
workload or #queues is equal to #cpus.

Redirect UDP packets generated by MoonGen between two virtio-net ports
through xdp_redirect show 37.4% (from 0.8Mpps to 1.1Mpps) improvement
compared to automatic steering policy since the overhead of flow
caches/hasing was totally eliminated.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/net/tun.c           | 33 ++++++++++++++++++++++++++++++++-
 include/uapi/linux/if_tun.h |  1 +
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1106521..03b4506 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -190,6 +190,20 @@ struct tun_steering_ops {
 			 u32 data);
 };
 
+void tun_steering_xmit_nop(struct tun_struct *tun, struct sk_buff *skb)
+{
+}
+
+u32 tun_steering_pre_rx_nop(struct tun_struct *tun, struct sk_buff *skb)
+{
+	return 0;
+}
+
+void tun_steering_post_rx_nop(struct tun_struct *tun, struct tun_file *tfile,
+			      u32 data)
+{
+}
+
 struct tun_flow_entry {
 	struct hlist_node hash_link;
 	struct rcu_head rcu;
@@ -571,6 +585,11 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 	return txq;
 }
 
+static u16 tun_cpu_select_queue(struct tun_struct *tun, struct sk_buff *skb)
+{
+	return smp_processor_id() % tun->numqueues;
+}
+
 static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
 			    void *accel_priv, select_queue_fallback_t fallback)
 {
@@ -2152,6 +2171,13 @@ static struct tun_steering_ops tun_automq_ops = {
 	.post_rx = tun_automq_post_rx,
 };
 
+static struct tun_steering_ops tun_cpu_ops = {
+	.select_queue = tun_cpu_select_queue,
+	.xmit = tun_steering_xmit_nop,
+	.pre_rx = tun_steering_pre_rx_nop,
+	.post_rx = tun_steering_post_rx_nop,
+};
+
 static int tun_flags(struct tun_struct *tun)
 {
 	return tun->flags & (TUN_FEATURES | IFF_PERSIST | IFF_TUN | IFF_TAP);
@@ -2775,6 +2801,9 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		case TUN_STEERING_AUTOMQ:
 			tun->steering_ops = &tun_automq_ops;
 			break;
+		case TUN_STEERING_CPU:
+			tun->steering_ops = &tun_cpu_ops;
+			break;
 		default:
 			ret = -EFAULT;
 		}
@@ -2784,6 +2813,8 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		ret = 0;
 		if (tun->steering_ops == &tun_automq_ops)
 			steering = TUN_STEERING_AUTOMQ;
+		else if (tun->steering_ops == &tun_cpu_ops)
+			steering = TUN_STEERING_CPU;
 		else
 			BUG();
 		if (copy_to_user(argp, &steering, sizeof(steering)))
@@ -2792,7 +2823,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 
 	case TUNGETSTEERINGFEATURES:
 		ret = 0;
-		steering = TUN_STEERING_AUTOMQ;
+		steering = TUN_STEERING_AUTOMQ | TUN_STEERING_CPU;
 		if (copy_to_user(argp, &steering, sizeof(steering)))
 			ret = -EFAULT;
 		break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 109760e..5f71d29 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -112,5 +112,6 @@ struct tun_filter {
 };
 
 #define TUN_STEERING_AUTOMQ 0x01 /* Automatic flow steering */
+#define TUN_STEERING_CPU    0x02 /* Processor id based flow steering */
 
 #endif /* _UAPI__IF_TUN_H */
-- 
2.7.4