busylock was added at the time we had expensive ticket spinlocks
(commit 79640a4ca6955e3ebdb7038508fa7a0cd7fa5527 ("net: add additional
lock to qdisc to increase throughput")
Now kernel spinlocks are MCS, this busylock things is no longer
relevant. It is slowing down things a bit.
With HTB qdisc, here are the numbers for 200 concurrent TCP_RR, on a host with
48 hyperthreads.
lpaa5:~# sar -n DEV 4 4 |grep eth0
10:05:44 eth0 798951.25 798951.75 52276.22 52275.26 0.00
0.00 0.50
10:05:48 eth0 798576.00 798572.75 52251.24 52250.39 0.00
0.00 0.75
10:05:52 eth0 798746.00 798748.75 52262.89 52262.13 0.00
0.00 0.50
10:05:56 eth0 798303.25 798291.50 52235.22 52233.10 0.00
0.00 0.50
Average: eth0 798644.12 798641.19 52256.39 52255.22 0.00
0.00 0.56
Disabling busylock (by using a local sysctl)
lpaa5:~# sar -n DEV 4 4 |grep eth0
10:05:14 eth0 864085.75 864091.50 56538.09 56537.46 0.00
0.00 0.50
10:05:18 eth0 864734.75 864729.25 56580.35 56579.05 0.00
0.00 0.75
10:05:22 eth0 864366.00 864361.50 56556.74 56555.00 0.00
0.00 0.50
10:05:26 eth0 864246.50 864248.75 56549.19 56547.65 0.00
0.00 0.50
Average: eth0 864358.25 864357.75 56556.09 56554.79 0.00
0.00 0.56
That would be a 8 % increase.
