Commit 2359a476 authored Jul 29, 2012 by Eric Dumazet Committed by David S. Miller Aug 10, 2012

codel: refine one condition to 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.

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 55461ddb

include/net/codel.h

+6 −2

Original line number	Diff line number	Diff line
		@@ -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.