Linux tool enables Resizable BAR for Intel Arc on older motherboards

Developer Rod Burlamaqui has released arc-rebar, a Linux tool that enables Resizable BAR for Intel Arc GPUs on motherboards lacking a ReBAR option. Arc cards rely heavily on the feature for good performance. The tool runs from the initramfs at every boot, before the GPU driver loads, without changing the BIOS, kernel or Intel’s drivers. Unlike ReBarUEFI, it does not require adding a module to motherboard firmware.

The workaround addresses the PCIe switch built into Arc cards, whose small upstream BAR prevents Linux from expanding the GPU’s memory window. It writes the card’s ReBAR register, then removes and rescans the root port. Intel engineers have proposed a kernel-level solution, but it has not yet been merged.

Testing on a Supermicro X9DRH-7TF with dual Xeon E5-2670 v2 CPUs and a 2015 BIOS expanded a B580’s CPU-visible VRAM from 256 MiB to a 16 GiB window covering all 12 GB. Measured VRAM bandwidth rose from 15 GB/s to 392 GB/s. A 4K Vulkan blur workload that previously stalled ran at 39 to 50 FPS.