From: Leslie Monis <lesliemonis@gmail.com>
Date: Thu, 28 Feb 2019 12:36:54 +0000 (+0530)
Subject: net: sched: pie: avoid slow division in drop probability decay
X-Git-Tag: v5.1-rc1~178^2~53
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6c97da141528097eb8e1d532dc0dbe3501f4c8ff;p=thirdparty%2Fkernel%2Flinux.git

net: sched: pie: avoid slow division in drop probability decay

As per RFC 8033, it is sufficient for the drop probability
decay factor to have a value of (1 - 1/64) instead of 98%.
This avoids the need to do slow division.

Suggested-by: David Laight <David.Laight@aculab.com>
Signed-off-by: Leslie Monis <lesliemonis@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index f93cfe034c729..1cc0c7b74aa35 100644
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -429,7 +429,8 @@ static void calculate_probability(struct Qdisc *sch)
 	 */
 
 	if (qdelay == 0 && qdelay_old == 0 && update_prob)
-		q->vars.prob = 98 * div_u64(q->vars.prob, 100);
+		/* Reduce drop probability to 98.4% */
+		q->vars.prob -= q->vars.prob / 64u;
 
 	q->vars.qdelay = qdelay;
 	q->vars.qlen_old = qlen;