Re: [Qemu-devel] 答复: 答复: 答复: question abo ut performance of dataplane

[Abel Gordon]

张磊强 <address@hidden> wrote on 07/04/2013 07:10:24 PM:

>
> HI, Abel & Stefan:
>
>      After thinking twice about the benchmarks and the idea of
> dataplane, I am still confused.

Please note while I am familiar with the documentation and architecture
of dataplane, I didn't contribute to the dataplane code. So Stefan is
actually the right person to answer your questions.

>      It's my understanding that the advantage of dataplane mainly
> includes two parts. The first is that splitting the IO thread from
> vcpu thread will avoid the global mutex competition, and the second
> is that the individual IO thread will not be blocked when "vm exit"
> occurs in vcpu thread.  Am I right?

As far as I understand you are right. But wait for Stefan's confirmation.

>      These two advantages will always be effective whether the vcpus
> is more than host's cores or not.

I would say that the advantage is effective as far as at least one vcpu
thread executing guest I/O runs simultaneously with the back-end
I/O thread (each thread on a different core).


> But why the advantage of dataplane
> is only so obvious when vcpus is more than host's cores?

Maybe the issue is related to the fact that no-dataplane experiences
more bottlenecks when your run more and more VCPU threads. So it not
that dataplane performs better with more VCPUs, the issue is that
no-dataplane performs worse with more VCPUs.