On 12/01/2010 11:34 PM, Stefan Hajnoczi wrote:
>> The guest CPU utilization numbers include an efficiency metric: %vcpu
>> per MB/sec. Here we see significant improvements too. Guests that
>> previously couldn't get more CPU work done now have regained some
>> breathing space.
>
> Thanks for those numbers. The guest improvements were expected, but the
> host numbers surprised me. Do you have an explanation as to why total host
> load should decrease?
The first vcpu does virtqueue kick - it holds the guest driver
vblk->lock across kick. Before this kick completes a second vcpu
tries to acquire vblk->lock, finds it is contended, and spins. So
we're burning CPU due to the long vblk->lock hold times.
With virtio-ioeventfd those kick times are reduced an there is less
contention on vblk->lock.
Makes sense.
--
error compiling committee.c: too many arguments to function
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