Re: [PATCH 00/13] deprecate pcommit

From: Andy Lutomirski
Date: Sun Jun 05 2016 - 13:41:52 EST

On Jun 4, 2016 1:53 PM, "Dan Williams" <dan.j.williams@xxxxxxxxx> wrote:
> Platforms supporting NVDIMMs are now required to provide persistence
> guarantees once pmem stores are accepted by the memory subsystem.

Can you point us to a precise definition of what exactly constitutes
stores being "accepted by the memory subsystem"? Back when pcommit
was a thing (hah!), it was precisely documented in the SDM.

> is usually achieved by a platform-level feature known as ADR
> (Asynchronous DRAM Refresh) that flushes any memory subsystem write
> pending queues on power loss/shutdown.

Blech. Does this mean that we need some NMI handler or similar that
does wbinvd? Will CPU caches automatically write themselves back on
power loss? Will we lose data if something goes wrong with an SMI

> The 'pcommit' instruction (which has not shipped on any product) is no
> longer needed and is deprecated.

Does this mean it will never ship?