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net: make default TX queue length a defined constant

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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>
This commit is contained in:
Jesper Dangaard Brouer 2016-11-03 14:56:01 +01:00 committed by David S. Miller
parent fc13fd3986
commit d0a81f67cd
2 changed files with 4 additions and 1 deletions
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2
include/net/pkt_sched.h
View File

@ -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;

3
net/ethernet/eth.c
View File

@ -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;