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netem: markov loss model transition fix

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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>
This commit is contained in:
Hagen Paul Pfeifer 2013-10-22 23:27:06 +02:00 committed by David S. Miller
parent b45bd46dec
commit 4a3ad7b3ea
1 changed files with 0 additions and 1 deletions
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1
net/sched/sch_netem.c
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@ -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;