Commit 0c850344 authored by Toke Høiland-Jørgensen's avatar Toke Høiland-Jørgensen Committed by David S. Miller
Browse files

sch_cake: Conditionally split GSO segments 



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: default avatarToke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a729b7f0

net/sched/sch_cake.c

+73 −26
Original line number Diff line number Diff line
@@ -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
@@ -1650,6 +1651,42 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
	if (unlikely(len > b->max_skblen))

		b->max_skblen = len;



	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;



		segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);

		if (IS_ERR_OR_NULL(segs))

			return qdisc_drop(skb, sch, to_free);



		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);



			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 {

		/* not splitting */

		cobalt_set_enqueue_time(skb, now);

		get_cobalt_cb(skb)->adjusted_len = cake_overhead(q, skb);

		flow_queue_add(flow, skb);
@@ -1680,6 +1717,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
		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:

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