From: Hagen Paul Pfeifer <hagen@jauu.net>
Date: Tue, 22 Oct 2013 21:27:06 +0000 (+0200)
Subject: netem: markov loss model transition fix
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=4a3ad7b3eade08ad1c760aaa4fe06a36f2584939;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

netem: markov loss model transition fix

The transition from markov state "3 => lost packets within a burst
period" to "1 => successfully transmitted packets within a gap period"
has no *additional* loss event. The loss already happen for transition
from 1 -> 3, this additional loss will make things go wild.

E.g. transition probabilities:

p13:   10%
p31:  100%

Expected:

Ploss = p13 / (p13 + p31)
Ploss = ~9.09%

... but it isn't. Even worse: we get a double loss - each time.
So simple don't return true to indicate loss, rather break and return
false.

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Stefano Salsano <stefano.salsano@uniroma2.it>
Cc: Fabio Ludovici <fabio.ludovici@yahoo.it>
Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index b87e83d07478..75c94e59a3bd 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -235,7 +235,6 @@ static bool loss_4state(struct netem_sched_data *q)
 			clg->state = 2;
 		else if (clg->a3 < rnd && rnd < clg->a2 + clg->a3) {
 			clg->state = 1;
-			return true;
 		} else if (clg->a2 + clg->a3 < rnd) {
 			clg->state = 3;
 			return true;