Subject: [PATCH net-next 5/8] net: sched: pie: add more conditions to auto-tune alpha and beta

From: Leslie Monis <[email-masked]>
Date: Wed, 31 Oct 2018 21:49:29 +0530

From: "Mohit P. Tahiliani" <[email-masked]>

The update in drop probability depends on the parameters
alpha and beta, which in turn reflect the current congestion
level. However, the previous if-else cases were recommended
when the supported bandwidth was up to 12 Mbps but, current
data links support a much higher bandwidth, and the
requirement for more bandwidth is in never-ending demand.
Hence, RFC 8033 suggests using more if-else cases for better
fine-tuning of parameters alpha and beta in order to control
the congestion as much as possible.

Signed-off-by: Mohit P. Tahiliani <[email-masked]>
Signed-off-by: Dhaval Khandla <[email-masked]>
Signed-off-by: Hrishikesh Hiraskar <[email-masked]>
Signed-off-by: Manish Kumar B <[email-masked]>
Signed-off-by: Sachin D. Patil <[email-masked]>
Signed-off-by: Leslie Monis <[email-masked]>
---
 net/sched/sch_pie.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index f4e189a..c84e91e 100644
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -343,10 +343,30 @@ static void calculate_probability(struct Qdisc *sch)
 	 * appropriately 2) scaling down by 16 to come to 0-2 range.
 	 * Please see paper for details.
 	 *
-	 * We scale alpha and beta differently depending on whether we are in
-	 * light, medium or high dropping mode.
+	 * We scale alpha and beta differently depending on how heavy the
+	 * congestion is.
 	 */
-	if (q->vars.prob < MAX_PROB / 100) {
+	if (q->vars.prob < MAX_PROB / 1000000) {
+		alpha =
+		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 15;
+		beta =
+		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 15;
+	} else if (q->vars.prob < MAX_PROB / 100000) {
+		alpha =
+		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 13;
+		beta =
+		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 13;
+	} else if (q->vars.prob < MAX_PROB / 10000) {
+		alpha =
+		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 11;
+		beta =
+		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 11;
+	} else if (q->vars.prob < MAX_PROB / 1000) {
+		alpha =
+		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 9;
+		beta =
+		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 9;
+	} else if (q->vars.prob < MAX_PROB / 100) {
 		alpha =
 		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 		beta =
-- 
2.7.4