Messages in this thread | | | Date | Mon, 26 Mar 2018 10:41:29 -0600 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory |
| |
On Mon, Mar 26, 2018 at 12:11:38PM +0100, Jonathan Cameron wrote: > On Tue, 13 Mar 2018 10:43:55 -0600 > Logan Gunthorpe <logang@deltatee.com> wrote: > > > On 12/03/18 09:28 PM, Sinan Kaya wrote: > > > On 3/12/2018 3:35 PM, Logan Gunthorpe wrote: > > > Regarding the switch business, It is amazing how much trouble you went into > > > limit this functionality into very specific hardware. > > > > > > I thought that we reached to an agreement that code would not impose > > > any limits on what user wants. > > > > > > What happened to all the emails we exchanged? > > > > It turns out that root ports that support P2P are far less common than > > anyone thought. So it will likely have to be a white list. > > This came as a bit of a surprise to our PCIe architect.
I don't think it is a hardware problem.
I know Mellanox and Nvidia have been doing p2p on Intel root complexes for something like 5-6 years now.. I don't have the details, but it does seem to work.
I have heard some chips give poor performance..
Also AMD GPU SLI uses P2P these days, so this isn't exactly a niche feature in Intel/AMD land.
I think the main issue here is that there is some BIOS involvement to set things up properly. Eg in GPU land motherboards certify for 'crossfire' support.
> His follow up was whether it was worth raising an ECR for the PCIe spec > to add a capability bit to allow this to be discovered. This might > long term avoid the need to maintain the white list for new devices.
If it is primarily a BIOS issue then it should be an ACPI thing, right?
Jason
| |