Speakers
Description
The kernel uses a whitelist do determine whether peer-to-peer DMA is supported between devices. But constantly amending the whitelist is a maintenance burden.
We are proposing to extend the ACPI HMAT table with bandwidth and latency characteristics for P2PDMA traffic between PCI host bridges (and between devices below the same host bridge).
This will remove the need for a whitelist.
It also closes a gap in virtualization: VMs have no visibility of the physical PCI topology and thus cannot determine P2PDMA reachability. The proposed HMAT extension solves this: VMMs such as qemu may present a synthesized HMAT table to VMs which reflects the physical capabilities. This replaces prior proposals such as Nvidia's Virtual Peer-to-Peer Approval Capability.
Last not least, the proposed HMAT extension allows users to populate PCI slots for optimal P2PDMA performance.
We will briefly present the draft of this ACPI Code First ECN and explain how it fits into the Linux P2PDMA model and path-selection algorithm. Afterwards we hope for a lively discussion on its merits.