Commit eeb84aa0 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net_sched: sch_fq: do not assume EDT packets are ordered 



TCP stack makes sure packets for a given flow are monotically
increasing, but we want to allow UDP packets to use EDT as
well, so that QUIC servers can use in-kernel pacing.

This patch adds a per-flow rb-tree on which packets might
be stored. We still try to use the linear list for the
typical cases where packets are queued with monotically
increasing skb->tstamp, since queue/dequeue packets on
a standard list is O(1).

Note that the ability to store packets in arbitrary EDT
order will allow us to implement later a per TCP socket
mechanism adding delays (with jitter eventually) and reorders,
to implement convenient network emulators.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a55a385d

net/sched/sch_fq.c

+83 −12
Original line number Diff line number Diff line
@@ -54,10 +54,23 @@ 
#include <net/tcp_states.h>

#include <net/tcp.h>



struct fq_skb_cb {

	u64	        time_to_send;

};



static inline struct fq_skb_cb *fq_skb_cb(struct sk_buff *skb)

{

	qdisc_cb_private_validate(skb, sizeof(struct fq_skb_cb));

	return (struct fq_skb_cb *)qdisc_skb_cb(skb)->data;

}



/*

 * Per flow structure, dynamically allocated

 * Per flow structure, dynamically allocated.

 * If packets have monotically increasing time_to_send, they are placed in O(1)

 * in linear list (head,tail), otherwise are placed in a rbtree (t_root).

 */

struct fq_flow {

	struct rb_root	t_root;

	struct sk_buff	*head;		/* list of skbs for this flow : first skb */

	union {

		struct sk_buff *tail;	/* last skb in the list */
@@ -298,6 +311,8 @@ static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q) 
		q->stat_allocation_errors++;

		return &q->internal;

	}

	/* f->t_root is already zeroed after kmem_cache_zalloc() */



	fq_flow_set_detached(f);

	f->sk = sk;

	if (skb->sk)
@@ -312,14 +327,40 @@ static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q) 
	return f;

}



static struct sk_buff *fq_peek(struct fq_flow *flow)

{

	struct sk_buff *skb = skb_rb_first(&flow->t_root);

	struct sk_buff *head = flow->head;



	if (!skb)

		return head;



	if (!head)

		return skb;



	if (fq_skb_cb(skb)->time_to_send < fq_skb_cb(head)->time_to_send)

		return skb;

	return head;

}



static void fq_erase_head(struct Qdisc *sch, struct fq_flow *flow,

			  struct sk_buff *skb)

{

	if (skb == flow->head) {

		flow->head = skb->next;

	} else {

		rb_erase(&skb->rbnode, &flow->t_root);

		skb->dev = qdisc_dev(sch);

	}

}



/* remove one skb from head of flow queue */

static struct sk_buff *fq_dequeue_head(struct Qdisc *sch, struct fq_flow *flow)

{

	struct sk_buff *skb = flow->head;

	struct sk_buff *skb = fq_peek(flow);



	if (skb) {

		flow->head = skb->next;

		fq_erase_head(sch, flow, skb);

		skb_mark_not_on_list(skb);

		flow->qlen--;

		qdisc_qstats_backlog_dec(sch, skb);
@@ -330,15 +371,36 @@ static struct sk_buff *fq_dequeue_head(struct Qdisc *sch, struct fq_flow *flow) 


static void flow_queue_add(struct fq_flow *flow, struct sk_buff *skb)

{

	struct sk_buff *head = flow->head;

	struct rb_node **p, *parent;

	struct sk_buff *head, *aux;



	skb->next = NULL;

	fq_skb_cb(skb)->time_to_send = skb->tstamp ?: ktime_get_ns();



	head = flow->head;

	if (!head ||

	    fq_skb_cb(skb)->time_to_send >= fq_skb_cb(flow->tail)->time_to_send) {

		if (!head)

			flow->head = skb;

		else

			flow->tail->next = skb;



		flow->tail = skb;

		skb->next = NULL;

		return;

	}



	p = &flow->t_root.rb_node;

	parent = NULL;



	while (*p) {

		parent = *p;

		aux = rb_to_skb(parent);

		if (fq_skb_cb(skb)->time_to_send >= fq_skb_cb(aux)->time_to_send)

			p = &parent->rb_right;

		else

			p = &parent->rb_left;

	}

	rb_link_node(&skb->rbnode, parent, p);

	rb_insert_color(&skb->rbnode, &flow->t_root);

}



static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
@@ -450,9 +512,9 @@ begin: 
		goto begin;

	}



	skb = f->head;

	skb = fq_peek(f);

	if (skb) {

		u64 time_next_packet = max_t(u64, ktime_to_ns(skb->tstamp),

		u64 time_next_packet = max_t(u64, fq_skb_cb(skb)->time_to_send,

					     f->time_next_packet);



		if (now < time_next_packet) {
@@ -533,6 +595,15 @@ out: 


static void fq_flow_purge(struct fq_flow *flow)

{

	struct rb_node *p = rb_first(&flow->t_root);



	while (p) {

		struct sk_buff *skb = rb_to_skb(p);



		p = rb_next(p);

		rb_erase(&skb->rbnode, &flow->t_root);

		rtnl_kfree_skbs(skb, skb);

	}

	rtnl_kfree_skbs(flow->head, flow->tail);

	flow->head = NULL;

	flow->qlen = 0;

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