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Subject: Re: [RFC] virtio-pmem: PMEM device spec
On 11.04.19 11:12, Pankaj Gupta wrote: > >>>> 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? Well there has to be a way to indicate how to flush writes, no? > > Thanks, > Pankaj > -- Thanks, David / dhildenb
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