Re: [Qemu-devel] What is the cause of -net socket, mcast bad performance?

[Stefan Hajnoczi]

On Thu, Aug 16, 2012 at 10:38 AM, Марк Коренберг <address@hidden> wrote:
> On my PC, tap <--> bridge <--> tap networking gives 600 megbit.
>
> Exactly the same, but -net socket,mcast  gives about 1 megbit (!) I do not
> understand why.
>
> In my mind, -net socket,mcast is the same as tap, but ethernet frames are
> going in much simplier way: instead of
>
> qemu1 -> /dev/tun -> kernel/bridge -> /dev/tun -> qemu2
>
> in such way:
>
> qemu1 -> qemu2
>
>
> Does somebody knows, why -net socket,mcast works so slowly?
>
> People said, that VDE performace is like TAP. Why not to make same
> performace on -net socket,mcast ?

600 -> 1 Mbit/s performance difference is larger than expected.

Can you post more details?
1. qemu and Linux kernel versions
2. qemu command-lines for your tap and mcast setups
3. Which benchmark and the command-line to run the test

Stefan