Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

From: Avi Kivity
Date: Mon Dec 21 2009 - 10:43:44 EST


On 12/21/2009 05:34 PM, Gregory Haskins wrote:

I think it would be fair to point out that these patches have been objected to
by the KVM folks quite extensively,
Actually, these patches have nothing to do with the KVM folks. You are
perhaps confusing this with the hypervisor-side discussion, of which
there is indeed much disagreement.

This is true, though these drivers are fairly pointless for virtualization without the host side support.

I did have a few issues with the guest drivers:
- the duplication of effort wrt virtio. These drivers don't cover exactly the same problem space, but nearly so.
- no effort at scalability - all interrupts are taken on one cpu
- the patches introduce a new virtual interrupt controller for dubious (IMO) benefits

From my research, the reason why virt in general, and KVM in particular
suffers on the IO performance front is as follows: IOs
(traps+interrupts) are more expensive than bare-metal, and real hardware
is naturally concurrent (your hbas and nics are effectively parallel
execution engines, etc).

Assuming my observations are correct, in order to squeeze maximum
performance from a given guest, you need to do three things: A)
eliminate as many IOs as you possibly can, B) reduce the cost of the
ones you can't avoid, and C) run your algorithms in parallel to emulate
concurrent silicon.

All these are addressed by vhost-net without introducing new drivers.

--
error compiling committee.c: too many arguments to function

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