On 26/03/18 10:41 AM, Jason Gunthorpe wrote:

On Mon, Mar 26, 2018 at 12:11:38PM +0100, Jonathan Cameron wrote:

quoted

On Tue, 13 Mar 2018 10:43:55 -0600
Logan Gunthorpe [off-list ref] wrote:

quoted

On 12/03/18 09:28 PM, Sinan Kaya wrote:

quoted

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.

The latest and greatest Power9 CPUs still explicitly do not support
this. And, if I recall correctly, the ARM64 device we played with did
not either -- but I suspect that will differ depending on vendor.

The latest Intel devices of course do support it, but go back 3-4 years
or so and the performance is pretty much unusable (at least for the
purposes of what this patchset implements). Even older CPUs did not
support it.

We haven't done any testing on AMD devices but I assume they are similar
to Intel.

In any case, even if every CPU manufactured today supported it well,
there are still older devices out there without support that we need to
ensure are handled properly.

Logan