On 2018-12-04 7:31 p.m., Jerome Glisse wrote: > How can i express multiple link, or memory that is only accessible > by a subset of the devices/CPUs. In today model they are back in > assumption like everyone can access all the node which do not hold > in what i am trying to do. Well multiple links are easy when you have a 'link' bus. Just add another link device under the bus. Technically, the accessibility issue is already encoded in sysfs. For example, through the PCI tree you can determine which ACS bits are set and determine which devices are behind the same root bridge the same way we do in the kernel p2pdma subsystem. This is all bus specific which is fine, but if we want to change that, we should have a common way for existing buses to describe these attributes in the existing tree. The new 'link' bus devices would have to have some way to describe cases if memory isn't accessible in some way across it. But really, I would say the kernel is responsible for telling you when memory is accessible to a list of initiators, so it should be part of the checks in a theoretical hbind api. This is already the approach p2pdma takes in-kernel: we have functions that tell you if two PCI devices can talk to each other and we have functions to give you memory accessible by a set of devices. What we don't have is a special tree that p2pdma users have to walk through to determine accessibility. In my eye's, you are just conflating a bunch of different issues that are better solved independently in the existing frameworks we have. And if they were tackled individually, you'd have a much easier time getting them merged one by one. Logan
