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@@ -0,0 +1,217 @@
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+From 712639929912c5eefb09facccb48d55b3f72c9f8 Mon Sep 17 00:00:00 2001
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+From: George Amanakis <[email protected]>
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+Date: Fri, 1 Mar 2019 16:04:05 +0100
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+Subject: [PATCH] sch_cake: Make the dual modes fairer
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+MIME-Version: 1.0
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+Content-Type: text/plain; charset=UTF-8
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+Content-Transfer-Encoding: 8bit
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+
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+CAKE host fairness does not work well with TCP flows in dual-srchost and
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+dual-dsthost setup. The reason is that ACKs generated by TCP flows are
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+classified as sparse flows, and affect flow isolation from other hosts. Fix
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+this by calculating host_load based only on the bulk flows a host
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+generates. In a hash collision the host_bulk_flow_count values must be
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+decremented on the old hosts and incremented on the new ones *if* the queue
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+is in the bulk set.
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+
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+Reported-by: Pete Heist <[email protected]>
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+Signed-off-by: George Amanakis <[email protected]>
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+Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
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+Signed-off-by: David S. Miller <[email protected]>
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+Signed-off-by: Kevin Darbyshire-Bryant <[email protected]>
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+---
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+ net/sched/sch_cake.c | 92 ++++++++++++++++++++++++++++++--------------
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+ 1 file changed, 63 insertions(+), 29 deletions(-)
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+
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+--- a/net/sched/sch_cake.c
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++++ b/net/sched/sch_cake.c
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+@@ -138,8 +138,8 @@ struct cake_flow {
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+ struct cake_host {
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+ u32 srchost_tag;
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+ u32 dsthost_tag;
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+- u16 srchost_refcnt;
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+- u16 dsthost_refcnt;
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++ u16 srchost_bulk_flow_count;
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++ u16 dsthost_bulk_flow_count;
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+ };
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+
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+ struct cake_heap_entry {
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+@@ -746,8 +746,10 @@ skip_hash:
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+ * queue, accept the collision, update the host tags.
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+ */
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+ q->way_collisions++;
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+- q->hosts[q->flows[reduced_hash].srchost].srchost_refcnt--;
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+- q->hosts[q->flows[reduced_hash].dsthost].dsthost_refcnt--;
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++ if (q->flows[outer_hash + k].set == CAKE_SET_BULK) {
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++ q->hosts[q->flows[reduced_hash].srchost].srchost_bulk_flow_count--;
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++ q->hosts[q->flows[reduced_hash].dsthost].dsthost_bulk_flow_count--;
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++ }
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+ allocate_src = cake_dsrc(flow_mode);
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+ allocate_dst = cake_ddst(flow_mode);
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+ found:
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+@@ -767,13 +769,14 @@ found:
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+ }
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+ for (i = 0; i < CAKE_SET_WAYS;
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+ i++, k = (k + 1) % CAKE_SET_WAYS) {
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+- if (!q->hosts[outer_hash + k].srchost_refcnt)
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++ if (!q->hosts[outer_hash + k].srchost_bulk_flow_count)
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+ break;
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+ }
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+ q->hosts[outer_hash + k].srchost_tag = srchost_hash;
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+ found_src:
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+ srchost_idx = outer_hash + k;
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+- q->hosts[srchost_idx].srchost_refcnt++;
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++ if (q->flows[reduced_hash].set == CAKE_SET_BULK)
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++ q->hosts[srchost_idx].srchost_bulk_flow_count++;
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+ q->flows[reduced_hash].srchost = srchost_idx;
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+ }
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+
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+@@ -789,13 +792,14 @@ found_src:
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+ }
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+ for (i = 0; i < CAKE_SET_WAYS;
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+ i++, k = (k + 1) % CAKE_SET_WAYS) {
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+- if (!q->hosts[outer_hash + k].dsthost_refcnt)
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++ if (!q->hosts[outer_hash + k].dsthost_bulk_flow_count)
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+ break;
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+ }
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+ q->hosts[outer_hash + k].dsthost_tag = dsthost_hash;
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+ found_dst:
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+ dsthost_idx = outer_hash + k;
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+- q->hosts[dsthost_idx].dsthost_refcnt++;
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++ if (q->flows[reduced_hash].set == CAKE_SET_BULK)
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++ q->hosts[dsthost_idx].dsthost_bulk_flow_count++;
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+ q->flows[reduced_hash].dsthost = dsthost_idx;
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+ }
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+ }
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+@@ -1793,20 +1797,30 @@ static s32 cake_enqueue(struct sk_buff *
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+ b->sparse_flow_count++;
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+
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+ if (cake_dsrc(q->flow_mode))
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+- host_load = max(host_load, srchost->srchost_refcnt);
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++ host_load = max(host_load, srchost->srchost_bulk_flow_count);
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+
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+ if (cake_ddst(q->flow_mode))
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+- host_load = max(host_load, dsthost->dsthost_refcnt);
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++ host_load = max(host_load, dsthost->dsthost_bulk_flow_count);
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+
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+ flow->deficit = (b->flow_quantum *
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+ quantum_div[host_load]) >> 16;
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+ } else if (flow->set == CAKE_SET_SPARSE_WAIT) {
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++ struct cake_host *srchost = &b->hosts[flow->srchost];
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++ struct cake_host *dsthost = &b->hosts[flow->dsthost];
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++
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+ /* this flow was empty, accounted as a sparse flow, but actually
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+ * in the bulk rotation.
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+ */
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+ flow->set = CAKE_SET_BULK;
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+ b->sparse_flow_count--;
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+ b->bulk_flow_count++;
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++
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++ if (cake_dsrc(q->flow_mode))
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++ srchost->srchost_bulk_flow_count++;
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++
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++ if (cake_ddst(q->flow_mode))
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++ dsthost->dsthost_bulk_flow_count++;
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++
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+ }
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+
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+ if (q->buffer_used > q->buffer_max_used)
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+@@ -1974,23 +1988,8 @@ retry:
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+ dsthost = &b->hosts[flow->dsthost];
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+ host_load = 1;
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+
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+- if (cake_dsrc(q->flow_mode))
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+- host_load = max(host_load, srchost->srchost_refcnt);
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+-
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+- if (cake_ddst(q->flow_mode))
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+- host_load = max(host_load, dsthost->dsthost_refcnt);
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+-
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+- WARN_ON(host_load > CAKE_QUEUES);
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+-
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+ /* flow isolation (DRR++) */
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+ if (flow->deficit <= 0) {
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+- /* The shifted prandom_u32() is a way to apply dithering to
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+- * avoid accumulating roundoff errors
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+- */
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+- flow->deficit += (b->flow_quantum * quantum_div[host_load] +
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+- (prandom_u32() >> 16)) >> 16;
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+- list_move_tail(&flow->flowchain, &b->old_flows);
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+-
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+ /* Keep all flows with deficits out of the sparse and decaying
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+ * rotations. No non-empty flow can go into the decaying
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+ * rotation, so they can't get deficits
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+@@ -1999,6 +1998,13 @@ retry:
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+ if (flow->head) {
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+ b->sparse_flow_count--;
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+ b->bulk_flow_count++;
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++
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++ if (cake_dsrc(q->flow_mode))
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++ srchost->srchost_bulk_flow_count++;
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++
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++ if (cake_ddst(q->flow_mode))
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++ dsthost->dsthost_bulk_flow_count++;
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++
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+ flow->set = CAKE_SET_BULK;
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+ } else {
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+ /* we've moved it to the bulk rotation for
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+@@ -2008,6 +2014,22 @@ retry:
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+ flow->set = CAKE_SET_SPARSE_WAIT;
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+ }
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+ }
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++
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++ if (cake_dsrc(q->flow_mode))
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++ host_load = max(host_load, srchost->srchost_bulk_flow_count);
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++
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++ if (cake_ddst(q->flow_mode))
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++ host_load = max(host_load, dsthost->dsthost_bulk_flow_count);
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++
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++ WARN_ON(host_load > CAKE_QUEUES);
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++
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++ /* The shifted prandom_u32() is a way to apply dithering to
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++ * avoid accumulating roundoff errors
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++ */
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++ flow->deficit += (b->flow_quantum * quantum_div[host_load] +
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++ (prandom_u32() >> 16)) >> 16;
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++ list_move_tail(&flow->flowchain, &b->old_flows);
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++
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+ goto retry;
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+ }
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+
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+@@ -2028,6 +2050,13 @@ retry:
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+ &b->decaying_flows);
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+ if (flow->set == CAKE_SET_BULK) {
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+ b->bulk_flow_count--;
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++
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++ if (cake_dsrc(q->flow_mode))
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++ srchost->srchost_bulk_flow_count--;
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++
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++ if (cake_ddst(q->flow_mode))
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++ dsthost->dsthost_bulk_flow_count--;
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++
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+ b->decaying_flow_count++;
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+ } else if (flow->set == CAKE_SET_SPARSE ||
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+ flow->set == CAKE_SET_SPARSE_WAIT) {
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+@@ -2041,14 +2070,19 @@ retry:
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+ if (flow->set == CAKE_SET_SPARSE ||
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+ flow->set == CAKE_SET_SPARSE_WAIT)
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+ b->sparse_flow_count--;
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+- else if (flow->set == CAKE_SET_BULK)
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++ else if (flow->set == CAKE_SET_BULK) {
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+ b->bulk_flow_count--;
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+- else
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++
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++ if (cake_dsrc(q->flow_mode))
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++ srchost->srchost_bulk_flow_count--;
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++
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++ if (cake_ddst(q->flow_mode))
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++ dsthost->dsthost_bulk_flow_count--;
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++
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++ } else
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+ b->decaying_flow_count--;
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+
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+ flow->set = CAKE_SET_NONE;
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+- srchost->srchost_refcnt--;
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+- dsthost->dsthost_refcnt--;
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+ }
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+ goto begin;
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+ }
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