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

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Date:	Thu, 05 Apr 2007 09:19:27 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Anthony Liguori <aliguori@...ibm.com>,
	kvm-devel@...ts.sourceforge.net, netdev <netdev@...r.kernel.org>
Subject: Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work

On Wed, 2007-04-04 at 23:21 +0200, Ingo Molnar wrote:
> * Anthony Liguori <aliguori@...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.



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