sch_sfq: avoid giving spurious NET_XMIT_CN signals

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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 <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Jarek Poplawski <jarkao2@gmail.com>
CC: Jamal Hadi Salim <hadi@cyberus.ca>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

...

This commit is contained in:

Eric Dumazet 2011-05-23 11:02:42 +00:00 • committed by David S. Miller

parent a4910b7444

commit 8efa885406

1 changed files with 6 additions and 2 deletions

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net/sched/sch_sfq.c

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