Re: Scalability of interface creation and deletion

Le samedi 07 mai 2011 à 20:42 +0200, Eric Dumazet a écrit :

Here is my trace here for one device deletion on one 8 core machine

[  800.447012] synchronize_rcu() in 15787 us
[  800.455013] synchronize_rcu() in 7682 us
[  800.464019] rcu_barrier() in 8487 us

Not that bad.

$ grep RCU .config
# RCU Subsystem
CONFIG_TREE_RCU=y
# CONFIG_PREEMPT_RCU is not set
CONFIG_RCU_TRACE=y
CONFIG_RCU_FANOUT=32
# CONFIG_RCU_FANOUT_EXACT is not set
# CONFIG_RCU_FAST_NO_HZ is not set
CONFIG_TREE_RCU_TRACE=y

By the way, if I change HZ from 1000 to 100 I now have ten times slower
result :

# ip link add link eth0 eth0.103 type vlan id 103
# time ip link del eth0.103

real	0m0.430s
user	0m0.000s
sys	0m0.000s

So all this is related to your HZ value, even in a CONFIG_NO_HZ=y
kernel. Alex, I guess you have HZ=250 ?

# uname -a
Linux svivoipvnx021 2.6.39-rc6-00214-g5511a34-dirty #574 SMP Sun May 8
08:44:14 CEST 2011 x86_64 x86_64 x86_64 GNU/Linux
# cat /proc/cmdline

I enabled CONFIG_RCU_FAST_NO_HZ and got worse results (but not
alsways... its very variable)

# time ip link del eth0.103

real	0m0.544s
user	0m0.000s
sys	0m0.000s


# time ip link del eth0.103

real	0m0.414s
user	0m0.000s
sys	0m0.000s