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sch_cake: Conditionally split GSO segments

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At lower bandwidths, the transmission time of a single GSO segment can add
an unacceptable amount of latency due to HOL blocking. Furthermore, with a
software shaper, any tuning mechanism employed by the kernel to control the
maximum size of GSO segments is thrown off by the artificial limit on
bandwidth. For this reason, we split GSO segments into their individual
packets iff the shaper is active and configured to a bandwidth <= 1 Gbps.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Toke Høiland-Jørgensen 2018-07-06 17:37:19 +02:00 committed by David S. Miller
parent a729b7f0bd
commit 0c850344d3
1 changed files with 72 additions and 25 deletions
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97
net/sched/sch_cake.c
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@ -80,6 +80,7 @@
#define CAKE_QUEUES (1024)
#define CAKE_FLOW_MASK 63
#define CAKE_FLOW_NAT_FLAG 64
#define CAKE_SPLIT_GSO_THRESHOLD (125000000) /* 1Gbps */
/* struct cobalt_params - contains codel and blue parameters
* @interval: codel initial drop rate
@ -1650,36 +1651,73 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
if (unlikely(len > b->max_skblen))
b->max_skblen = len;
cobalt_set_enqueue_time(skb, now);
get_cobalt_cb(skb)->adjusted_len = cake_overhead(q, skb);
flow_queue_add(flow, skb);
if (skb_is_gso(skb) && q->rate_flags & CAKE_FLAG_SPLIT_GSO) {
struct sk_buff *segs, *nskb;
netdev_features_t features = netif_skb_features(skb);
unsigned int slen = 0;
if (q->ack_filter)
ack = cake_ack_filter(q, flow);
segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
if (IS_ERR_OR_NULL(segs))
return qdisc_drop(skb, sch, to_free);
if (ack) {
b->ack_drops++;
sch->qstats.drops++;
b->bytes += qdisc_pkt_len(ack);
len -= qdisc_pkt_len(ack);
q->buffer_used += skb->truesize - ack->truesize;
if (q->rate_flags & CAKE_FLAG_INGRESS)
cake_advance_shaper(q, b, ack, now, true);
while (segs) {
nskb = segs->next;
segs->next = NULL;
qdisc_skb_cb(segs)->pkt_len = segs->len;
cobalt_set_enqueue_time(segs, now);
get_cobalt_cb(segs)->adjusted_len = cake_overhead(q,
segs);
flow_queue_add(flow, segs);
qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(ack));
consume_skb(ack);
sch->q.qlen++;
slen += segs->len;
q->buffer_used += segs->truesize;
b->packets++;
segs = nskb;
}
/* stats */
b->bytes += slen;
b->backlogs[idx] += slen;
b->tin_backlog += slen;
sch->qstats.backlog += slen;
q->avg_window_bytes += slen;
qdisc_tree_reduce_backlog(sch, 1, len);
consume_skb(skb);
} else {
sch->q.qlen++;
q->buffer_used += skb->truesize;
}
/* not splitting */
cobalt_set_enqueue_time(skb, now);
get_cobalt_cb(skb)->adjusted_len = cake_overhead(q, skb);
flow_queue_add(flow, skb);
/* stats */
b->packets++;
b->bytes += len;
b->backlogs[idx] += len;
b->tin_backlog += len;
sch->qstats.backlog += len;
q->avg_window_bytes += len;
if (q->ack_filter)
ack = cake_ack_filter(q, flow);
if (ack) {
b->ack_drops++;
sch->qstats.drops++;
b->bytes += qdisc_pkt_len(ack);
len -= qdisc_pkt_len(ack);
q->buffer_used += skb->truesize - ack->truesize;
if (q->rate_flags & CAKE_FLAG_INGRESS)
cake_advance_shaper(q, b, ack, now, true);
qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(ack));
consume_skb(ack);
} else {
sch->q.qlen++;
q->buffer_used += skb->truesize;
}
/* stats */
b->packets++;
b->bytes += len;
b->backlogs[idx] += len;
b->tin_backlog += len;
sch->qstats.backlog += len;
q->avg_window_bytes += len;
}
if (q->overflow_timeout)
cake_heapify_up(q, b->overflow_idx[idx]);
@ -2531,6 +2569,11 @@ static int cake_change(struct Qdisc *sch, struct nlattr *opt,
if (tb[TCA_CAKE_MEMORY])
q->buffer_config_limit = nla_get_u32(tb[TCA_CAKE_MEMORY]);
if (q->rate_bps && q->rate_bps <= CAKE_SPLIT_GSO_THRESHOLD)
q->rate_flags |= CAKE_FLAG_SPLIT_GSO;
else
q->rate_flags &= ~CAKE_FLAG_SPLIT_GSO;
if (q->tins) {
sch_tree_lock(sch);
cake_reconfigure(sch);
@ -2686,6 +2729,10 @@ static int cake_dump(struct Qdisc *sch, struct sk_buff *skb)
if (nla_put_u32(skb, TCA_CAKE_MPU, q->rate_mpu))
goto nla_put_failure;
if (nla_put_u32(skb, TCA_CAKE_SPLIT_GSO,
!!(q->rate_flags & CAKE_FLAG_SPLIT_GSO)))
goto nla_put_failure;
return nla_nest_end(skb, opts);
nla_put_failure: