Commit d0a81f67 authored Nov 03, 2016 by Jesper Dangaard Brouer Committed by David S. Miller Nov 07, 2016

net: make default TX queue length a defined constant

The default TX queue length of Ethernet devices have been a magic
constant of 1000, ever since the initial git import.

Looking back in historical trees[1][2] the value used to be 100,
with the same comment "Ethernet wants good queues". The commit[3]
that changed this from 100 to 1000 didn't describe why, but from
conversations with Robert Olsson it seems that it was changed
when Ethernet devices went from 100Mbit/s to 1Gbit/s, because the
link speed increased x10 the queue size were also adjusted.  This
value later caused much heartache for the bufferbloat community.

This patch merely moves the value into a defined constant.

[1] https://git.kernel.org/cgit/linux/kernel/git/davem/netdev-vger-cvs.git/
[2] https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/
[3] https://git.kernel.org/tglx/history/c/98921832c232



Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent fc13fd39

include/net/pkt_sched.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -6,6 +6,8 @@
		#include <linux/if_vlan.h>
		#include <net/sch_generic.h>

		#define DEFAULT_TX_QUEUE_LEN 1000

		struct qdisc_walker {
		int stop;
		int skip;

net/ethernet/eth.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -62,6 +62,7 @@
		#include <net/dsa.h>
		#include <net/flow_dissector.h>
		#include <linux/uaccess.h>
		#include <net/pkt_sched.h>

		__setup("ether=", netdev_boot_setup);

		@@ -359,7 +360,7 @@ void ether_setup(struct net_device *dev)
		dev->min_mtu = ETH_MIN_MTU;
		dev->max_mtu = ETH_DATA_LEN;
		dev->addr_len = ETH_ALEN;
		dev->tx_queue_len = 1000; /* Ethernet wants good queues */
		dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
		dev->flags = IFF_BROADCAST\|IFF_MULTICAST;
		dev->priv_flags \|= IFF_TX_SKB_SHARING;

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