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Subject: Re: [virtio-dev] Re: [PATCH v2] virtio-pmem: PMEM device spec
On Thu, 19 Aug 2021 at 11:39, Stefan Hajnoczi <stefanha@redhat.com> wrote: > > 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 > persistence). Sure. will remove this then. > > 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. Thanks. Maybe internally they would be doing CPU flushes (a guess) and/or some metadata sync operation. Thank you for all the feedback. Will send a v3 with the suggested changes. Best regards, Pankaj > > Stefan
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