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Subject: Re: [virtio-dev] Re: [PATCH v2] virtio-pmem: PMEM device spec

On Thu, Aug 19, 2021 at 07:53:48AM +0200, Pankaj Gupta wrote:
> > >> > +\drivernormative{\subsubsection}{Driver Initialization: Virtio flush}{Device Types / PMEM Driver / Driver Initialization / Virtio flush}
> > >> > +
> > >> > +The driver MUST implement a virtio based flushing interface.
> > >>
> > >> I think this can be dropped. The only way to make writes persistent is
> > >> by sending flush requests. There is no need to say that the driver has
> > >> to use this interface. It doesn't really have to, but then it won't be
> > >> able to guarantee persistence.
> > >
> > > I am not 100 percent sure on this.
> >
> > I don't think we want this in a normative section, but maybe there's a
> > place for it in a section that describes the general operation?
> I was saying because this is the must property for virtio-pmem device
> which is emulated
> on regular block device. virtio-pmem above real persistent devices
> don't need any explicit flush.
> This can be enhanced later for real persistent devices which don't
> need explicit flush
> and thus driver writers don't have to worry about it.

A feature bit can be added in the future that hints to the driver that
flushes are not necessary (only CPU cache flushes are required for

However, I remember seeing specifications for persistent memory devices
that do require explicit flush operations (not just a CPU cache flush).
Let's keep them in mind too.


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