On 12/22/2009 10:21 AM, Andi Kleen wrote:
So far, the only actual technical advantage I've seen is that vbus avoids
EOI exits.
The technical advantage is that it's significantly faster today.
There are two separate pieces of code in question. There are front-end
drivers and there are back-end drivers.
Right now, there are only front-end drivers in the kernel today. The
combination of vbus front-end drivers and *kernel* back-end drivers are
faster than the *combination* of virtio front-end drivers and
*userspace* back-end drivers.
vhost-net is our kernel back-end driver. No one has yet established
that the combination of virtio front-end driver and kernel back-end
driver is really significantly slower than vbus.
Maybe your proposed alternative is as fast, or maybe it's not. Who knows?
We think we understand why vbus does better than the current userspace
virtio backend. That's why we're building vhost-net. It's not done yet,
but our expectation is that it will do just as well if not better.
That's the vapourware vs working code disconnect I mentioned. One side has hard
numbers&working code and the other has expectations. I usually find it sad when the
vapourware holds up the working code.
We're not talking about vaporware. vhost-net exists.
Regards,
Anthony Liguori
-Andi
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