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From b8fc328668a74e1314a19266755a54abd875e5a6 Mon Sep 17 00:00:00 2001
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From: Eric Dumazet <edumazet@google.com>
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Date: Sun, 29 Jul 2012 20:52:21 +0000
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Subject: [PATCH] codel: refine one condition to avoid a nul rec_inv_sqrt
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commit 2359a47671fc4fb0fe5e9945f76c2cb10792c0f8 upstream.
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One condition before codel_Newton_step() was not good if
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we never left the dropping state for a flow. As a result
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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
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many packets before reaching 'target' and recovering from this problem.
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To keep codel_vars_init() as efficient as possible, refine
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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
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a fix.
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Reported-by: Anton Mich <lp2s1h@gmail.com>
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Signed-off-by: Eric Dumazet <edumazet@google.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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---
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include/net/codel.h | 8 ++++++--
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1 file changed, 6 insertions(+), 2 deletions(-)
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--- a/include/net/codel.h
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+++ b/include/net/codel.h
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@@ -305,6 +305,8 @@ static struct sk_buff *codel_dequeue(str
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}
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}
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} else if (drop) {
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+ u32 delta;
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+
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if (params->ecn && INET_ECN_set_ce(skb)) {
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stats->ecn_mark++;
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} else {
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@@ -320,9 +322,11 @@ static struct sk_buff *codel_dequeue(str
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* assume that the drop rate that controlled the queue on the
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* last cycle is a good starting point to control it now.
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*/
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- if (codel_time_before(now - vars->drop_next,
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+ delta = vars->count - vars->lastcount;
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+ if (delta > 1 &&
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+ codel_time_before(now - vars->drop_next,
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16 * params->interval)) {
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- vars->count = (vars->count - vars->lastcount) | 1;
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+ vars->count = delta;
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/* we dont care if rec_inv_sqrt approximation
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* is not very precise :
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* Next Newton steps will correct it quadratically.
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