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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: Pete Heist <peteheist@gmail.com>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
George Amanakis 2019-03-01 16:04:05 +01:00 committed by David S. Miller
parent c21e18a550
commit 7126399299
1 changed files with 63 additions and 29 deletions
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92
net/sched/sch_cake.c
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@ -138,8 +138,8 @@ struct cake_flow {
struct cake_host { struct cake_host {
u32 srchost_tag; u32 srchost_tag;
u32 dsthost_tag; u32 dsthost_tag;
u16 srchost_refcnt; u16 srchost_bulk_flow_count;
u16 dsthost_refcnt; u16 dsthost_bulk_flow_count;
}; };
struct cake_heap_entry { 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. * queue, accept the collision, update the host tags.
*/ */
q->way_collisions++; q->way_collisions++;
q->hosts[q->flows[reduced_hash].srchost].srchost_refcnt--; if (q->flows[outer_hash + k].set == CAKE_SET_BULK) {
q->hosts[q->flows[reduced_hash].dsthost].dsthost_refcnt--; 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_src = cake_dsrc(flow_mode);
allocate_dst = cake_ddst(flow_mode); allocate_dst = cake_ddst(flow_mode);
found: 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; for (i = 0; i < CAKE_SET_WAYS;
i++, k = (k + 1) % 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; break;
} }
q->hosts[outer_hash + k].srchost_tag = srchost_hash; q->hosts[outer_hash + k].srchost_tag = srchost_hash;
found_src: found_src:
srchost_idx = outer_hash + k; 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; 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; for (i = 0; i < CAKE_SET_WAYS;
i++, k = (k + 1) % 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; break;
} }
q->hosts[outer_hash + k].dsthost_tag = dsthost_hash; q->hosts[outer_hash + k].dsthost_tag = dsthost_hash;
found_dst: found_dst:
dsthost_idx = outer_hash + k; 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; 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++; b->sparse_flow_count++;
if (cake_dsrc(q->flow_mode)) 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)) 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 * flow->deficit = (b->flow_quantum *
quantum_div[host_load]) >> 16; quantum_div[host_load]) >> 16;
} else if (flow->set == CAKE_SET_SPARSE_WAIT) { } 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 /* this flow was empty, accounted as a sparse flow, but actually
* in the bulk rotation. * in the bulk rotation.
*/ */
flow->set = CAKE_SET_BULK; flow->set = CAKE_SET_BULK;
b->sparse_flow_count--; b->sparse_flow_count--;
b->bulk_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) 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]; dsthost = &b->hosts[flow->dsthost];
host_load = 1; 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++) */ /* flow isolation (DRR++) */
if (flow->deficit <= 0) { 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 /* Keep all flows with deficits out of the sparse and decaying
* rotations. No non-empty flow can go into the decaying * rotations. No non-empty flow can go into the decaying
* rotation, so they can't get deficits * rotation, so they can't get deficits
@ -2000,6 +1999,13 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
if (flow->head) { if (flow->head) {
b->sparse_flow_count--; b->sparse_flow_count--;
b->bulk_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; flow->set = CAKE_SET_BULK;
} else { } else {
/* we've moved it to the bulk rotation for /* 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; 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; goto retry;
} }
@ -2029,6 +2051,13 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
&b->decaying_flows); &b->decaying_flows);
if (flow->set == CAKE_SET_BULK) { if (flow->set == CAKE_SET_BULK) {
b->bulk_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--;
b->decaying_flow_count++; b->decaying_flow_count++;
} else if (flow->set == CAKE_SET_SPARSE || } else if (flow->set == CAKE_SET_SPARSE ||
flow->set == CAKE_SET_SPARSE_WAIT) { 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 || if (flow->set == CAKE_SET_SPARSE ||
flow->set == CAKE_SET_SPARSE_WAIT) flow->set == CAKE_SET_SPARSE_WAIT)
b->sparse_flow_count--; b->sparse_flow_count--;
else if (flow->set == CAKE_SET_BULK) else if (flow->set == CAKE_SET_BULK) {
b->bulk_flow_count--; 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--; b->decaying_flow_count--;
flow->set = CAKE_SET_NONE; flow->set = CAKE_SET_NONE;
srchost->srchost_refcnt--;
dsthost->dsthost_refcnt--;
} }
goto begin; goto begin;
} }