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Commit 37c0aead authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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net_sched: sch_fq: handle non connected flows 



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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent eeb84aa0

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;