From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH] sch_sfq: avoid giving spurious NET_XMIT_CN signals Date: Mon, 23 May 2011 23:02:42 +0200 Message-ID: <1306184562.2638.14.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev , Patrick McHardy , Jarek Poplawski , Jamal Hadi Salim , Stephen Hemminger To: David Miller Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:60760 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030336Ab1EWVCq (ORCPT ); Mon, 23 May 2011 17:02:46 -0400 Received: by wya21 with SMTP id 21so4515850wya.19 for ; Mon, 23 May 2011 14:02:45 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: While chasing a possible net_sched bug, I found that IP fragments have litle chance to pass a congestioned SFQ qdisc : - Say SFQ qdisc is full because one flow is non responsive. - ip_fragment() wants to send two fragments belonging to an idle flow. - sfq_enqueue() queues first packet, but see queue limit reached : - sfq_enqueue() drops one packet from 'big consumer', and returns NET_XMIT_CN. - ip_fragment() cancel remaining fragments. This patch restores fairness, making sure we return NET_XMIT_CN only if we dropped a packet from the same flow. Signed-off-by: Eric Dumazet CC: Patrick McHardy CC: Jarek Poplawski CC: Jamal Hadi Salim CC: Stephen Hemminger --- net/sched/sch_sfq.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c index 7ef87f9..b1d00f8 100644 --- a/net/sched/sch_sfq.c +++ b/net/sched/sch_sfq.c @@ -361,7 +361,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch) { struct sfq_sched_data *q = qdisc_priv(sch); unsigned int hash; - sfq_index x; + sfq_index x, qlen; struct sfq_slot *slot; int uninitialized_var(ret); @@ -405,8 +405,12 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch) if (++sch->q.qlen <= q->limit) return NET_XMIT_SUCCESS; + qlen = slot->qlen; sfq_drop(sch); - return NET_XMIT_CN; + /* Return Congestion Notification only if we dropped a packet + * from this flow. + */ + return (qlen != slot->qlen) ? NET_XMIT_CN : NET_XMIT_SUCCESS; } static struct sk_buff *