Intel Enabling Resizable BAR To Work With I/O Virtualization On Linux

Resizable BAR support (also known as ReBAR / AMD Smart Access Memory) has been popular with gamers for supported configurations for being able to improve GPU performance. Intel is now working on enabling the Linux kernel to support Resizable BAR when in the context of I/O Virtualization.

Resizable BAR is a PCI Express feature can allow for the entire vRAM contents to be accessible by the CPU rather than being limited to a 256MB window. In turn that can lead to more efficient transfers between the CPU and GPU, but is contingent upon CPU/GPU/system support. Linux has supported Resizable BAR behavior as part of the PCIe specification and various Linux graphics drivers do make use of Resizable BAR in capable system configurations.

The new patches being worked on by Intel are for enabling Resizable BAR support in the PCI VF (Virtual Function) code so that existing ReBAR query/enabling interface can work with I/O Virtualization (IOV) BAR as well. This in turn should be useful for those assigning a graphics card via SR-IOV for gaming within a virtual machine and the like to be able to enable Resizable BAR.

That in-progress Resizable BAR support for IOV can be found via this patch thread.