[Cake] [PATCH net-next] sch_cake: Make gso-splitting configurable from userspace

[Dave Taht]

This patch restores cake's deployed behavior at line rate to always
split gso, and makes gso splitting configurable from userspace.

running cake unlimited (unshaped) at 1gigE, local traffic:

no-split-gso bql limit: 131966
split-gso bql limit:   ~42392-45420 

On this 4 stream test splitting gso apart results in halving the
observed interpacket latency at no loss in throughput.

Summary of tcp_nup test run 'gso-split' (at 2018-07-26 16:03:51.824728):

 Ping (ms) ICMP :         0.83         0.81 ms              341
 TCP upload avg :       235.43       235.39 Mbits/s         301
 TCP upload sum :       941.71       941.56 Mbits/s         301
 TCP upload::1  :       235.45       235.43 Mbits/s         271
 TCP upload::2  :       235.45       235.41 Mbits/s         289
 TCP upload::3  :       235.40       235.40 Mbits/s         288
 TCP upload::4  :       235.41       235.40 Mbits/s         291

verses

Summary of tcp_nup test run 'no-split-gso' (at 2018-07-26 16:37:23.563960):

                           avg       median          # data pts
 Ping (ms) ICMP :         1.67         1.73 ms              348
 TCP upload avg :       234.56       235.37 Mbits/s         301
 TCP upload sum :       938.24       941.49 Mbits/s         301
 TCP upload::1  :       234.55       235.38 Mbits/s         285
 TCP upload::2  :       234.57       235.37 Mbits/s         286
 TCP upload::3  :       234.58       235.37 Mbits/s         274
 TCP upload::4  :       234.54       235.42 Mbits/s         288
---
 net/sched/sch_cake.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 539c949..35fc725 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -80,7 +80,6 @@
 #define CAKE_QUEUES (1024)
 #define CAKE_FLOW_MASK 63
 #define CAKE_FLOW_NAT_FLAG 64
-#define CAKE_SPLIT_GSO_THRESHOLD (125000000) /* 1Gbps */
 
 /* struct cobalt_params - contains codel and blue parameters
  * @interval:	codel initial drop rate
@@ -2569,10 +2568,12 @@ static int cake_change(struct Qdisc *sch, struct nlattr *opt,
 	if (tb[TCA_CAKE_MEMORY])
 		q->buffer_config_limit = nla_get_u32(tb[TCA_CAKE_MEMORY]);
 
-	if (q->rate_bps && q->rate_bps <= CAKE_SPLIT_GSO_THRESHOLD)
-		q->rate_flags |= CAKE_FLAG_SPLIT_GSO;
-	else
-		q->rate_flags &= ~CAKE_FLAG_SPLIT_GSO;
+	if (tb[TCA_CAKE_SPLIT_GSO]) {
+		if (!!nla_get_u32(tb[TCA_CAKE_SPLIT_GSO]))
+			q->rate_flags |= CAKE_FLAG_SPLIT_GSO;
+		else
+			q->rate_flags &= ~CAKE_FLAG_SPLIT_GSO;
+	}
 
 	if (q->tins) {
 		sch_tree_lock(sch);
@@ -2608,7 +2609,7 @@ static int cake_init(struct Qdisc *sch, struct nlattr *opt,
 	q->target   =   5000; /* 5ms: codel RFC argues
 			       * for 5 to 10% of interval
 			       */
-
+	q->rate_flags |= CAKE_FLAG_SPLIT_GSO;
 	q->cur_tin = 0;
 	q->cur_flow  = 0;
 
-- 
2.7.4