Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion

[Paolo Bonzini]

On 23/11/2017 17:14, Dan Williams wrote:
> On Wed, Nov 22, 2017 at 8:05 PM, Xiao Guangrong
> <address@hidden> wrote:
>>
>>
>> On 11/22/2017 02:19 AM, Rik van Riel wrote:
>>
>>> We can go with the "best" interface for what
>>> could be a relatively slow flush (fsync on a
>>> file on ssd/disk on the host), which requires
>>> that the flushing task wait on completion
>>> asynchronously.
>>
>>
>> I'd like to clarify the interface of "wait on completion
>> asynchronously" and KVM async page fault a bit more.
>>
>> Current design of async-page-fault only works on RAM rather
>> than MMIO, i.e, if the page fault caused by accessing the
>> device memory of a emulated device, it needs to go to
>> userspace (QEMU) which emulates the operation in vCPU's
>> thread.
>>
>> As i mentioned before the memory region used for vNVDIMM
>> flush interface should be MMIO and consider its support
>> on other hypervisors, so we do better push this async
>> mechanism into the flush interface design itself rather
>> than depends on kvm async-page-fault.
> 
> I would expect this interface to be virtio-ring based to queue flush
> requests asynchronously to the host.

Could we reuse the virtio-blk device, only with a different device id?

Thanks,

Paolo