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Codel: 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.

Brought over from 3.5-stable

Signed-off-by: Dave Taht <dave.taht@bufferbloat.net>

SVN-Revision: 32950
This commit is contained in:
John Crispin 2012-08-02 13:39:50 +00:00
parent c2d3274ffc
commit f45132d1d4
1 changed files with 68 additions and 0 deletions
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target/linux/generic/patches-3.3/049-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sqrt.patch Normal file
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From patchwork Mon Jul 30 06:52:21 2012
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: codel: refine one condition to avoid a nul rec_inv_sqrt
Date: Sun, 29 Jul 2012 20:52:21 -0000
From: Eric Dumazet <eric.dumazet@gmail.com>
X-Patchwork-Id: 173968
Message-Id: <1343631141.2626.13293.camel@edumazet-glaptop>
To: David Miller <davem@davemloft.net>
Cc: netdev <netdev@vger.kernel.org>, Anton Mich <lp2s1h@gmail.com>
From: Eric Dumazet <edumazet@google.com>
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 <lp2s1h@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
include/net/codel.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
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diff --git a/include/net/codel.h b/include/net/codel.h
index 550debf..389cf62 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.