Re: [RFC] virtio-pmem: PMEM device spec

[Pankaj Gupta <pagupta@redhat.com>]

> >> new file mode 100644
> >> index 0000000..04e07bb
> >> --- /dev/null
> >> +++ b/virtio-pmem.tex
> >> @@ -0,0 +1,134 @@
> >> +\section{PMEM Device}\label{sec:Device Types / PMEM Device}
> >> +
> >> +The virtio pmem is a fake persistent memory (NVDIMM) device
> >> +used to bypass the guest page cache and provide a virtio
> >> +based asynchronous flush mechanism. This avoids the need
> > 
> > Is there anything "fake" about virtio-pmem from the perspective of the
> > device interface?
> > 
> > What you are describing is one use case.  But on a platform that doesn't
> > have existing physical NVDIMM interfaces, ACPI, etc maybe virtio-pmem
> > would be used to pass through physical NVDIMMs from the host?  If you
> > agree, then it might make sense to describe the device simply as a
> > persistent memory device and give "fake NVDIMM" as an example use case
> > in a separate paragraph.  This would make the text more future-proof.
> 
> Very good point. E.g. on x86-64, we might want to pass a real NVDIMM to
> the guest using virtio-pmem, if our guest VM e.g. has no ACPI configured.
> 
> In this case, it would be helpful to indicate if the flushing interface
> is to be used, or if other flushing (e.g. like NVDIMMs) is to be used.
> 

Yes. Agree. This is a very good point, will consider pass-through of 
real NVDIMM device for architectures don't support ACPI.

Yes, corresponding flushing mechanism should be mentioned but I am not sure
if it should be mentioned in device specification?

Thanks,
Pankaj