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Commit 71263992 authored by George Amanakis's avatar George Amanakis Committed by David S. Miller
Browse files

sch_cake: Make the dual modes fairer 



CAKE host fairness does not work well with TCP flows in dual-srchost and
dual-dsthost setup. The reason is that ACKs generated by TCP flows are
classified as sparse flows, and affect flow isolation from other hosts. Fix
this by calculating host_load based only on the bulk flows a host
generates. In a hash collision the host_bulk_flow_count values must be
decremented on the old hosts and incremented on the new ones *if* the queue
is in the bulk set.

Reported-by: default avatarPete Heist <peteheist@gmail.com>
Signed-off-by: default avatarGeorge Amanakis <gamanakis@gmail.com>
Signed-off-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c21e18a5

net/sched/sch_cake.c

+63 −29
Original line number Diff line number Diff line
@@ -138,8 +138,8 @@ struct cake_flow { 
struct cake_host {

	u32 srchost_tag;

	u32 dsthost_tag;

	u16 srchost_refcnt;

	u16 dsthost_refcnt;

	u16 srchost_bulk_flow_count;

	u16 dsthost_bulk_flow_count;

};



struct cake_heap_entry {
@@ -746,8 +746,10 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb, 
		 * queue, accept the collision, update the host tags.

		 */

		q->way_collisions++;

		q->hosts[q->flows[reduced_hash].srchost].srchost_refcnt--;

		q->hosts[q->flows[reduced_hash].dsthost].dsthost_refcnt--;

		if (q->flows[outer_hash + k].set == CAKE_SET_BULK) {

			q->hosts[q->flows[reduced_hash].srchost].srchost_bulk_flow_count--;

			q->hosts[q->flows[reduced_hash].dsthost].dsthost_bulk_flow_count--;

		}

		allocate_src = cake_dsrc(flow_mode);

		allocate_dst = cake_ddst(flow_mode);

found:
@@ -767,13 +769,14 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb, 
			}

			for (i = 0; i < CAKE_SET_WAYS;

				i++, k = (k + 1) % CAKE_SET_WAYS) {

				if (!q->hosts[outer_hash + k].srchost_refcnt)

				if (!q->hosts[outer_hash + k].srchost_bulk_flow_count)

					break;

			}

			q->hosts[outer_hash + k].srchost_tag = srchost_hash;

found_src:

			srchost_idx = outer_hash + k;

			q->hosts[srchost_idx].srchost_refcnt++;

			if (q->flows[reduced_hash].set == CAKE_SET_BULK)

				q->hosts[srchost_idx].srchost_bulk_flow_count++;

			q->flows[reduced_hash].srchost = srchost_idx;

		}
@@ -789,13 +792,14 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb, 
			}

			for (i = 0; i < CAKE_SET_WAYS;

			     i++, k = (k + 1) % CAKE_SET_WAYS) {

				if (!q->hosts[outer_hash + k].dsthost_refcnt)

				if (!q->hosts[outer_hash + k].dsthost_bulk_flow_count)

					break;

			}

			q->hosts[outer_hash + k].dsthost_tag = dsthost_hash;

found_dst:

			dsthost_idx = outer_hash + k;

			q->hosts[dsthost_idx].dsthost_refcnt++;

			if (q->flows[reduced_hash].set == CAKE_SET_BULK)

				q->hosts[dsthost_idx].dsthost_bulk_flow_count++;

			q->flows[reduced_hash].dsthost = dsthost_idx;

		}

	}
@@ -1794,20 +1798,30 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
		b->sparse_flow_count++;



		if (cake_dsrc(q->flow_mode))

			host_load = max(host_load, srchost->srchost_refcnt);

			host_load = max(host_load, srchost->srchost_bulk_flow_count);



		if (cake_ddst(q->flow_mode))

			host_load = max(host_load, dsthost->dsthost_refcnt);

			host_load = max(host_load, dsthost->dsthost_bulk_flow_count);



		flow->deficit = (b->flow_quantum *

				 quantum_div[host_load]) >> 16;

	} else if (flow->set == CAKE_SET_SPARSE_WAIT) {

		struct cake_host *srchost = &b->hosts[flow->srchost];

		struct cake_host *dsthost = &b->hosts[flow->dsthost];



		/* this flow was empty, accounted as a sparse flow, but actually

		 * in the bulk rotation.

		 */

		flow->set = CAKE_SET_BULK;

		b->sparse_flow_count--;

		b->bulk_flow_count++;



		if (cake_dsrc(q->flow_mode))

			srchost->srchost_bulk_flow_count++;



		if (cake_ddst(q->flow_mode))

			dsthost->dsthost_bulk_flow_count++;



	}



	if (q->buffer_used > q->buffer_max_used)
@@ -1975,23 +1989,8 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
	dsthost = &b->hosts[flow->dsthost];

	host_load = 1;



	if (cake_dsrc(q->flow_mode))

		host_load = max(host_load, srchost->srchost_refcnt);



	if (cake_ddst(q->flow_mode))

		host_load = max(host_load, dsthost->dsthost_refcnt);



	WARN_ON(host_load > CAKE_QUEUES);



	/* flow isolation (DRR++) */

	if (flow->deficit <= 0) {

		/* The shifted prandom_u32() is a way to apply dithering to

		 * avoid accumulating roundoff errors

		 */

		flow->deficit += (b->flow_quantum * quantum_div[host_load] +

				  (prandom_u32() >> 16)) >> 16;

		list_move_tail(&flow->flowchain, &b->old_flows);



		/* Keep all flows with deficits out of the sparse and decaying

		 * rotations.  No non-empty flow can go into the decaying

		 * rotation, so they can't get deficits
@@ -2000,6 +1999,13 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
			if (flow->head) {

				b->sparse_flow_count--;

				b->bulk_flow_count++;



				if (cake_dsrc(q->flow_mode))

					srchost->srchost_bulk_flow_count++;



				if (cake_ddst(q->flow_mode))

					dsthost->dsthost_bulk_flow_count++;



				flow->set = CAKE_SET_BULK;

			} else {

				/* we've moved it to the bulk rotation for
@@ -2009,6 +2015,22 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
				flow->set = CAKE_SET_SPARSE_WAIT;

			}

		}



		if (cake_dsrc(q->flow_mode))

			host_load = max(host_load, srchost->srchost_bulk_flow_count);



		if (cake_ddst(q->flow_mode))

			host_load = max(host_load, dsthost->dsthost_bulk_flow_count);



		WARN_ON(host_load > CAKE_QUEUES);



		/* The shifted prandom_u32() is a way to apply dithering to

		 * avoid accumulating roundoff errors

		 */

		flow->deficit += (b->flow_quantum * quantum_div[host_load] +

				  (prandom_u32() >> 16)) >> 16;

		list_move_tail(&flow->flowchain, &b->old_flows);



		goto retry;

	}
@@ -2029,6 +2051,13 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
					       &b->decaying_flows);

				if (flow->set == CAKE_SET_BULK) {

					b->bulk_flow_count--;



					if (cake_dsrc(q->flow_mode))

						srchost->srchost_bulk_flow_count--;



					if (cake_ddst(q->flow_mode))

						dsthost->dsthost_bulk_flow_count--;



					b->decaying_flow_count++;

				} else if (flow->set == CAKE_SET_SPARSE ||

					   flow->set == CAKE_SET_SPARSE_WAIT) {
@@ -2042,14 +2071,19 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
				if (flow->set == CAKE_SET_SPARSE ||

				    flow->set == CAKE_SET_SPARSE_WAIT)

					b->sparse_flow_count--;

				else if (flow->set == CAKE_SET_BULK)

				else if (flow->set == CAKE_SET_BULK) {

					b->bulk_flow_count--;

				else



					if (cake_dsrc(q->flow_mode))

						srchost->srchost_bulk_flow_count--;



					if (cake_ddst(q->flow_mode))

						dsthost->dsthost_bulk_flow_count--;



				} else

					b->decaying_flow_count--;



				flow->set = CAKE_SET_NONE;

				srchost->srchost_refcnt--;

				dsthost->dsthost_refcnt--;

			}

			goto begin;

		}