On Tue, Nov 23, 2010 at 10:13:43AM +0800, lidong chen wrote:
> 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).
At this point, I'd suggest testing vhost-net on the upstream kernel,
not on rhel kernels. The change that introduced per-device threads is:
c23f3445e68e1db0e74099f264bc5ff5d55ebdeb
> 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%.
Is CONFIG_SCHED_DEBUG set? We are stressing the scheduler a lot with
vhost-net.
> 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.
Let's try to figure out what the issue is, first.
--
MST
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