Hi Neel,

Thank you very much for your response -

That's great!

I guess this should deliver the full capacity for basically any IO system around, be it a fast SSD or ramdisk. (Since the guest may not need to flush data immediately to the host, I guess read performance is the more sensitive point.)

Which disk emulation mode is best for a BSD guest, "virtio-blk" or "ahci-hd"?

In general, should any other consideration be made for performance (using the "direct" or "nocache" BHyVe configuration options, particular consideration for proper sector alignment when using a disk image stored on the host's SSD-based ZFS, mounting the host ZFS filesystem with "noatime")?

Kind regards,
Tinker

On 2015-05-10 04:03, Neel Natu wrote:
Hi Tinker,

On Sat, May 9, 2015 at 9:49 AM, Tinker <ti...@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The wiki is out of date.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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