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sch_cake: Make the dual modes fairer
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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>
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@gamanakis @davem330
gamanakis authored and davem330 committed Mar 4, 2019
1 parent c21e18a commit 7126399
Showing 1 changed file with 63 additions and 29 deletions.
92 changes: 63 additions & 29 deletions net/sched/sch_cake.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand Down Expand Up @@ -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:
Expand All @@ -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;
}

Expand All @@ -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;
}
}
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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
Expand All @@ -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
Expand All @@ -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;
}

Expand All @@ -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) {
Expand All @@ -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;
}
Expand Down

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