Re: Accelerating non-standard disk types

[Paolo Bonzini]

On 5/16/22 19:38, Raphael Norwitz wrote:
> [1] Keep using the SCSI translation in QEMU but back vDisks with a
> vhost-user-scsi or vhost-user-blk backend device.
> [2] Implement SATA and IDE emulation with vfio-user (likely with an SPDK
> client?).
> [3] We've also been looking at your libblkio library. From your
> description in
> https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg06146.html  it
> sounds like it may definitely play a role here, and possibly provide the
> nessesary abstractions to back I/O from these emulated disks to any
> backends we may want?

First of all: have you benchmarked it?  How much time is spent on MMIO 
vs. disk I/O?

Of the options above, the most interesting to me is to implement a 
vhost-user-blk/vhost-user-scsi backend in QEMU, similar to the NVMe one, 
that would translate I/O submissions to virtqueue (including polling and 
the like) and could be used with SATA.

For IDE specifically, I'm not sure how much it can be sped up since it 
has only 1 in-flight operation.  I think using KVM coalesced I/O could 
provide an interesting boost (assuming instant or near-instant reply 
from the backend).  If all you're interested in however is not really 
performance, but rather having a single "connection" to your back end, 
vhost-user is certainly an option.

Paolo