From 2359a47671fc4fb0fe5e9945f76c2cb10792c0f8 Mon Sep 17 00:00:00 2001
From: Eric Dumazet
Date: Sun, 29 Jul 2012 20:52:21 +0000
Subject: codel: refine one condition to avoid a nul rec_inv_sqrt
One condition before codel_Newton_step() was not good if
we never left the dropping state for a flow. As a result
rec_inv_sqrt was 0, instead of the ~0 initial value.
codel control law was then set to a very aggressive mode, dropping
many packets before reaching 'target' and recovering from this problem.
To keep codel_vars_init() as efficient as possible, refine
the condition to make sure rec_inv_sqrt initial value is correct
Many thanks to Anton Mich for discovering the issue and suggesting
a fix.
Reported-by: Anton Mich
Signed-off-by: Eric Dumazet
Signed-off-by: David S. Miller
---
include/net/codel.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/include/net/codel.h b/include/net/codel.h
index 550debfc240..389cf621161 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -305,6 +305,8 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
}
}
} else if (drop) {
+ u32 delta;
+
if (params->ecn && INET_ECN_set_ce(skb)) {
stats->ecn_mark++;
} else {
@@ -320,9 +322,11 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
* assume that the drop rate that controlled the queue on the
* last cycle is a good starting point to control it now.
*/
- if (codel_time_before(now - vars->drop_next,
+ delta = vars->count - vars->lastcount;
+ if (delta > 1 &&
+ codel_time_before(now - vars->drop_next,
16 * params->interval)) {
- vars->count = (vars->count - vars->lastcount) | 1;
+ vars->count = delta;
/* we dont care if rec_inv_sqrt approximation
* is not very precise :
* Next Newton steps will correct it quadratically.
--
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