Re: your mail

Chaitanya Kulkarni
2019-03-19T23:49:24Z

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.
>
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