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

[Pankaj Gupta <pagupta@redhat.com>]

> >>>> --- /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?
> 
> Well there has to be a way to indicate how to flush writes, no?

yes. 

Thanks,
Pankaj

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