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authorJohn Crispin <john@openwrt.org>2012-08-02 13:39:50 +0000
committerJohn Crispin <john@openwrt.org>2012-08-02 13:39:50 +0000
commitf45132d1d444ec33df3938e3e2a78ebee750ed8b (patch)
tree39cfe2ed4ad3336d827fa5317067a753e2d335cc /target
parentc2d3274ffcfdd5711c791b8ddafae3eea3207f06 (diff)
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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
Diffstat (limited to 'target')
-rw-r--r--target/linux/generic/patches-3.3/049-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sqrt.patch68
1 files changed, 68 insertions, 0 deletions
diff --git a/target/linux/generic/patches-3.3/049-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sqrt.patch b/target/linux/generic/patches-3.3/049-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sqrt.patch
new file mode 100644
index 0000000..210a58c
--- /dev/null
+++ b/target/linux/generic/patches-3.3/049-codel-refine-one-condition-to-avoid-a-nul-rec_inv_sqrt.patch
@@ -0,0 +1,68 @@
+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.