Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work

[Rusty Russell <rusty@rustcorp.com.au>]

On Wed, 2007-04-04 at 23:21 +0200, Ingo Molnar wrote:
> * Anthony Liguori <aliguori@us.ibm.com> wrote:
> 
> > But why is it a good thing to do PV drivers in the kernel?  You lose 
> > flexibility and functionality to gain performance. [...]
> 
> in Linux a kernel-space network driver can still be tunneled over 
> user-space code, and hence you can add arbitrary add-on functionality 
> (and thus have flexibility), without slowing down the common case (which 
> would be to tunnel the guest's network traffic into the firewall rules 
> of the kernel. No need to touch user-space for any of that).

You didn't quote Anthony's point about "it's more about there not being
good enough userspace interfaces to do network IO."

It's easier to write a kernel-space network driver, but it's not
obviously the right thing to do until we can show that an efficient
packet-level userspace interface isn't possible.  I don't think that's
been done, and it would be interesting to try.

Cheers,
Rusty.