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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
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...inux/generic/patches-3.3/049-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sqrt.patch
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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> | ||
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From: Eric Dumazet <edumazet@google.com> | ||
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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. | ||
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codel control law was then set to a very aggressive mode, dropping | ||
many packets before reaching 'target' and recovering from this problem. | ||
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To keep codel_vars_init() as efficient as possible, refine | ||
the condition to make sure rec_inv_sqrt initial value is correct | ||
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Many thanks to Anton Mich for discovering the issue and suggesting | ||
a fix. | ||
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Reported-by: Anton Mich <lp2s1h@gmail.com> | ||
Signed-off-by: Eric Dumazet <edumazet@google.com> | ||
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--- | ||
include/net/codel.h | 8 ++++++-- | ||
1 file changed, 6 insertions(+), 2 deletions(-) | ||
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-- | ||
To unsubscribe from this list: send the line "unsubscribe netdev" in | ||
the body of a message to majordomo@vger.kernel.org | ||
More majordomo info at http://vger.kernel.org/majordomo-info.html | ||
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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. |