net_sched: sch_fq: handle non connected flows (37c0aead) · Commits · 戴 / test

FQ packet scheduler assumed that packets could be classified based on their owning socket. This means that if a UDP server uses one UDP socket to send packets to different destinations, packets all land in one FQ flow. This is unfair, since each TCP flow has a unique bucket, meaning that in case of pressure (fully utilised uplink), TCP flows have more share of the bandwidth. If we instead detect unconnected sockets, we can use a stochastic hash based on the 4-tuple hash. This also means a QUIC server using one UDP socket will properly spread the outgoing packets to different buckets, and in-kernel pacing based on EDT model will no longer risk having big rb-tree on one flow. Note that UDP application might provide the skb->hash in an ancillary message at sendmsg() time to avoid the cost of a dissection in fq packet scheduler. Signed-off-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/sched/sch_fq.c

+13 −2

Original line number	Diff line number	Diff line
		@@ -270,6 +270,17 @@ static struct fq_flow fq_classify(struct sk_buff skb, struct fq_sched_data *q)
		*/
		sk = (struct sock *)((hash << 1) \| 1UL);
		skb_orphan(skb);
		} else if (sk->sk_state == TCP_CLOSE) {
		unsigned long hash = skb_get_hash(skb) & q->orphan_mask;
		/*
		* Sockets in TCP_CLOSE are non connected.
		* Typical use case is UDP sockets, they can send packets
		* with sendto() to many different destinations.
		* We probably could use a generic bit advertising
		* non connected sockets, instead of sk_state == TCP_CLOSE,
		* if we care enough.
		*/
		sk = (struct sock *)((hash << 1) \| 1UL);
		}

		root = &q->fq_root[hash_ptr(sk, q->fq_trees_log)];
		@@ -290,7 +301,7 @@ static struct fq_flow fq_classify(struct sk_buff skb, struct fq_sched_data *q)
		* It not, we need to refill credit with
		* initial quantum
		*/
		if (unlikely(skb->sk &&
		if (unlikely(skb->sk == sk &&
		f->socket_hash != sk->sk_hash)) {
		f->credit = q->initial_quantum;
		f->socket_hash = sk->sk_hash;
		@@ -315,7 +326,7 @@ static struct fq_flow fq_classify(struct sk_buff skb, struct fq_sched_data *q)

		fq_flow_set_detached(f);
		f->sk = sk;
		if (skb->sk)
		if (skb->sk == sk)
		f->socket_hash = sk->sk_hash;
		f->credit = q->initial_quantum;

Admin message