Re: [PATCH RFC 1/1] Add support for ZONE_DEVICE IO memory with struct pages.

Haggai Eran
2016-03-17T15:18:11Z

On 3/14/2016 11:57 PM, Jason Gunthorpe wrote:
> The other issue is that the fencing mechanism RDMA uses to create
> ordering with system memory is not good enough to fence peer-peer
> transactions in the general case. It is only possibly good enough if
> all the transactions run through the root complex.

Are you sure this is a problem? I'm not sure it is clear in the PCIe
specs, but I thought that for transactions that are not relaxed-ordered
and don't use ID-based ordering, a PCIe switch must prevent reads and
writes from passing writes. I assume this is true even when the requestor
ID is different because IDO relaxes these constraints specifically
for transactions coming from different requestor IDs.

Regards,
Haggai