Bhyve storage improvements (was: Several bhyve quirks)

[Alexander Motin]

> I've always assumed virtio driver > emulated driver so it didn't occur
> to me to try ahci-hd.

I've just merged to FreeBSD stable/10 branch set of bhyve changes that
should significantly improve situation in the storage area.

virtio-blk driver was fixed to work asynchronously and not block virtual
CPU, that should fix many problems with performance and interactivity.
Both virtio-blk and ahci-hd drivers got ability to execute multiple (up
to 8) requests same time, that should proportionally improve parallel
random I/O performance on wide storages.  At this point virtio-blk is
indeed faster then ahci-hd on high IOPS, and they both are faster then
before.

On the other side ahci-hd driver now got TRIM support to allow freeing
unused space on backing ZVOL. Unfortunately there is no any TRIM/UNMAP
support in virtio-blk API to allow the same.

Also both virtio-blk and ahci-hd drivers now report to guest logical and
physical block sizes of underlying storage, that allow guests properly
align partitions and I/Os for best compatibility and performance.

-- 
Alexander Motin