Re: your mail

Maxim Levitsky
2019-03-20T16:45:15Z

On Tue, 2019-03-19 at 23:49 +0000, Chaitanya Kulkarni wrote:
> Hi Keith,
> On 03/19/2019 08:21 AM, 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).
>
> I have the code for the NVMeOf target passthru-ctrl, I think we can use
> that as it is if you are looking for the passthru for NVMeOF.
>
> I'll post patch-series based on the latest code base soon.

I am very intersing in this code.
Could you explain how your NVMeOF target passthrough works?
Which components of the NVME stack does it involve?

Best regards,
Maxim Levitsky

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