I test the performance between per-vhost kthread disable and enable.
Test method:
Send the same traffic load between per-vhost kthread disable and
enable, and compare the cpu rate of host os.
I run five vm on kvm, each of them have five nic.
the vhost version which per-vhost kthread disable we used is rhel6
beta 2(2.6.32.60).
the vhost version which per-vhost kthread enable we used is rhel6 (2.6.32-71).
Test result:
with per-vhost kthread disable, the cpu rate of host os is 110%.
with per-vhost kthread enable, the cpu rate of host os is 130%.
In 2.6.32.60,the whole system only have a kthread.
[root@rhel6-kvm1 ~]# ps -ef | grep vhost
root 973 2 0 Nov22 ? 00:00:00 [vhost]
In 2.6.32.71,the whole system have 25 kthread.
[root@kvm-4slot ~]# ps -ef | grep vhost-
root 12896 2 0 10:26 ? 00:00:00 [vhost-12842]
root 12897 2 0 10:26 ? 00:00:00 [vhost-12842]
root 12898 2 0 10:26 ? 00:00:00 [vhost-12842]
root 12899 2 0 10:26 ? 00:00:00 [vhost-12842]
root 12900 2 0 10:26 ? 00:00:00 [vhost-12842]
root 13022 2 0 10:26 ? 00:00:00 [vhost-12981]
root 13023 2 0 10:26 ? 00:00:00 [vhost-12981]
root 13024 2 0 10:26 ? 00:00:00 [vhost-12981]
root 13025 2 0 10:26 ? 00:00:00 [vhost-12981]
root 13026 2 0 10:26 ? 00:00:00 [vhost-12981]
root 13146 2 0 10:26 ? 00:00:00 [vhost-13088]
root 13147 2 0 10:26 ? 00:00:00 [vhost-13088]
root 13148 2 0 10:26 ? 00:00:00 [vhost-13088]
root 13149 2 0 10:26 ? 00:00:00 [vhost-13088]
root 13150 2 0 10:26 ? 00:00:00 [vhost-13088]
...
Code difference:
In 2.6.32.60,in function vhost_init, create the kthread for vhost.
vhost_workqueue = create_singlethread_workqueue("vhost");
In 2.6.32.71,in function vhost_dev_set_owner, create the kthread for
each nic interface.
dev->wq = create_singlethread_workqueue(vhost_name);
Conclusion:
with per-vhost kthread enable, the system can more throughput.
but deal the same traffic load with per-vhost kthread enable, it waste
more cpu resource.
In my application scene, the cpu resource is more important, and one
kthread for deal with traffic load is enough.
So i think we should add a param to control this.
for the CPU-bound system, this param disable per-vhost kthread.
for the I/O-bound system, this param enable per-vhost kthread.
the default value of this param is enable.
If my opinion is right, i will give a patch for this.
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