Re: your mail

Maxim Levitsky
2019-04-08T10:04:16Z

On Tue, 2019-03-19 at 09:22 -0600, Keith Busch wrote:
> On Tue, Mar 19, 2019 at 04:41:07PM +0200, Maxim Levitsky wrote:
> > -> Share the NVMe device between host and guest.
> > Even in fully virtualized configurations,
> > some partitions of nvme device could be used by guests as block
> > devices
> > while others passed through with nvme-mdev to achieve balance between
> > all features of full IO stack emulation and performance.
> >
> > -> NVME-MDEV is a bit faster due to the fact that in-kernel driver
> > can send interrupts to the guest directly without a context
> > switch that can be expensive due to meltdown mitigation.
> >
> > -> Is able to utilize interrupts to get reasonable performance.
> > This is only implemented
> > as a proof of concept and not included in the patches,
> > but interrupt driven mode shows reasonable performance
> >
> > -> This is a framework that later can be used to support NVMe devices
> > with more of the IO virtualization built-in
> > (IOMMU with PASID support coupled with device that supports it)
>
> Would be very interested to see the PASID support. You wouldn't even
> need to mediate the IO doorbells or translations if assigning entire
> namespaces, and should be much faster than the shadow doorbells.
>
> I think you should send 6/9 "nvme/pci: init shadow doorbell after each
> reset" separately for immediate inclusion.
>
> I like the idea in principle, but it will take me a little time to get
> through reviewing your implementation. I would have guessed we could
> have leveraged something from the existing nvme/target for the mediating
> controller register access and admin commands. Maybe even start with
> implementing an nvme passthrough namespace target type (we currently
> have block and file).

Hi!

Sorry to bother you, but any update?

I was somewhat sick for the last week, now finally back in shape to continue
working on this and other tasks I have.

I am studing now the nvme target code and the io_uring to evaluate the
difficultiy of using something similiar to talk to the block device instead of /
in addtion to the direct connection I implemented.

I would be glad to hear more feedback on this project.

I will also soon post the few fixes separately as you suggested.

Best regards,
Maxim Levitskky