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 X-Patchwork-Id: 173968 Message-Id: <1343631141.2626.13293.camel@edumazet-glaptop> To: David Miller Cc: netdev , Anton Mich From: Eric Dumazet 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 Signed-off-by: Eric Dumazet --- include/net/codel.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) -- 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 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.