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From: Phil Sutter <phil@nwl.cc>
To: netdev@vger.kernel.org
Cc: Jesper Dangaard Brouer <brouer@redhat.com>,
	Cong Wang <cwang@twopensource.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	David Miller <davem@davemloft.net>
Subject: [net-next PATCH 2/3] net: sched: set tx_queue_len to default when changing noqueue device's qdisc
Date: Wed, 29 Jul 2015 22:51:42 +0200	[thread overview]
Message-ID: <1438203103-27013-3-git-send-email-phil@nwl.cc> (raw)
In-Reply-To: <1438203103-27013-2-git-send-email-phil@nwl.cc>

Virtual interfaces don't necessarily need a qdisc attached to them. This
is signalled by setting dev->tx_queue_len to zero upon initialisation. The
problems begin when a user still adds a qdisc, as then the special value
is used as a regular one causing massive packet drops as soon as the
device sees a bit of traffic load.

This patch solves the issue by setting tx_queue_len to the global
default for physical devices if it is zero and a qdisc is added. Another
benefit of this is that veth devices can default to noqueue while still
preserving the expected behaviour when adding a qdisc.

The drawback of this patch is that the noqueue state won't be restored
after a user has removed the custom qdisc, as the information about
whether this is legitimate for the given device is lost.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 net/sched/sch_api.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index f06aa01..79b8900 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1315,6 +1315,10 @@ graft:
 			qdisc_destroy(q);
 		return err;
 	}
+	/* circumvent noqueue hack for virtual interfaces if
+	 * user desires to use a qdisc on it */
+	if (!dev->tx_queue_len)
+		dev->tx_queue_len = CONFIG_DEFAULT_TX_QUEUE_LEN;
 
 	return 0;
 }
-- 
2.1.2

  reply	other threads:[~2015-07-29 20:51 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-29 20:51 [net-next PATCH 0/3] Backwards-compatible noqueue in virtual interfaces Phil Sutter
2015-07-29 20:51 ` [net-next PATCH 1/3] net: make default tx_queue_len configurable Phil Sutter
2015-07-29 20:51   ` Phil Sutter [this message]
2015-07-29 20:51     ` [net-next PATCH 3/3] veth: don't assign a qdisc to veth Phil Sutter
2015-07-29 21:10     ` [net-next PATCH 2/3] net: sched: set tx_queue_len to default when changing noqueue device's qdisc Florian Westphal
2015-07-29 21:10     ` Eric Dumazet
2015-07-29 22:08       ` Phil Sutter
2015-07-29 21:06   ` [net-next PATCH 1/3] net: make default tx_queue_len configurable Florian Westphal
2015-07-29 21:34     ` Phil Sutter
2015-07-29 21:37       ` David Miller
2015-08-11 15:48         ` Jesper Dangaard Brouer
2015-08-11 16:23           ` Phil Sutter
2015-08-12  1:13             ` Alexei Starovoitov
2015-08-12 14:55               ` Eric Dumazet
2015-08-13  1:13               ` Phil Sutter
2015-08-13 13:10                 ` Jesper Dangaard Brouer
2015-08-13 15:06                   ` Phil Sutter
2015-07-29 23:10 ` [net-next PATCH 0/3] Backwards-compatible noqueue in virtual interfaces Cong Wang

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