Is the BHyVe guest as suitable for high-performance disk IO as the host?

[Neel Natu]

Hi Tinker,

On Sat, May 9, 2015 at 9:49 AM, Tinker <tinkr at openmailbox.org> wrote:
> Hi!
>
> For an environment with very heavy parallell IO, should the performance be
> just as good in a BHyVe guest as in the FreeBSD host environment?
>
> What I thought of is that I guess within the host environment, the storage
> subsystem should have all kinds of optimizations like an internal work queue
> that pushes lots of work alinearly/asynchronously to the disk controller and
> this way allows it, in turn, to give all its performance.
>
> Does the virtualized disk interface carry over all that goodness to the
> guest?
>

bhyve creates 8 worker threads for each virtual disk controller (both
ahci and virtio-blk).

All guest I/O is handled asynchronously by these worker threads which
provide parallelism.

> (https://wiki.freebsd.org/bhyve seems to say yes, presuming you configure
> BHyVe to run the virtual disk in AHCI mode?)
>

The wiki is out of date.

Since r280037 the virtio-blk emulation also gets the benefits of using
the block_if worker threads.

best
Neel

> Thanks!
> Tinker
>
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