Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

Benjamin Herrenschmidt
2017-04-14T11:37:59Z

On Thu, 2017-04-13 at 22:40 -0600, Logan Gunthorpe wrote:
>
> On 13/04/17 10:16 PM, Jason Gunthorpe wrote:
> > I'd suggest just detecting if there is any translation in bus
> > addresses anywhere and just hard disabling P2P on such systems.
>
> That's a fantastic suggestion. It simplifies things significantly.
> Unless there are any significant objections I think I will plan on
> doing
> that.

I object.

> > On modern hardware with 64 bit BARs there is very little reason to
> > have translation, so I think this is a legacy feature.
>
> Yes, p2pmem users are likely to be designing systems around it (ie
> JBOFs) and not trying to shoehorn it onto legacy architectures.
>
> At the very least, it makes sense to leave it out and if someone
> comes
> along who cares they can put in the effort to support the address
> translation.
>
> Thanks,
>
> Logan