codel: refine one condition to avoid a nul rec_inv_sqrt
svn path=/dists/sid/linux/; revision=19403
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linux (3.2.30-2) UNRELEASED; urgency=low
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* codel: refine one condition to avoid a nul rec_inv_sqrt
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-- Ben Hutchings <ben@decadent.org.uk> Sat, 29 Sep 2012 14:19:46 +0200
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linux (3.2.30-1) unstable; urgency=low
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* New upstream stable update:
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@ -0,0 +1,53 @@
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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: 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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diff --git a/include/net/codel.h b/include/net/codel.h
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index 550debf..389cf62 100644
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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(struct Qdisc *sch,
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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(struct Qdisc *sch,
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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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@ -271,6 +271,7 @@ features/all/codel/0004-net-codel-Add-missing-include-linux-prefetch.h.patch
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features/all/codel/0005-net-codel-fix-build-errors.patch
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features/all/codel/0006-codel-use-u16-field-instead-of-31bits-for-rec_inv_sq.patch
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features/all/codel/0007-fq_codel-should-use-qdisc-backlog-as-threshold.patch
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features/all/codel/0008-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sq.patch
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# AppArmor userland compatibility. This had better be gone in wheezy+1!
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features/all/AppArmor-compatibility-patch-for-v5-interface.patch
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