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Subject[PATCH net-next 3/3] tun: introduce cpu id based steering policy
Date
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@redhat.com>
---
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
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