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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: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2019-05-04 16:48:54 -07:00 committed by David S. Miller
parent eeb84aa0d0
commit 37c0aead79
1 changed files with 13 additions and 2 deletions
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15
net/sched/sch_fq.c
View File

@ -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;