Intel Arc cards have always leaned heavily on Resizable BAR, to the point where Intel once told Alchemist buyers without it to stick with other vendors, and TechPowerUp's B580 review listed it as required for good performance. As spotted by Videocardz, developer Rod Burlamaqui has now released arc-rebar, a Linux tool that turns it on for Arc GPUs on motherboards that never got a ReBAR option. It runs from the initramfs at every boot, before the GPU driver loads, and doesn't touch the BIOS, kernel, or Intel's drivers. That sets it apart from earlier workarounds like ReBarUEFI, which has to be added to the motherboard's firmware.

The fix targets the PCIe switch built into Arc cards, whose small upstream BAR blocks Linux from enlarging the GPU's memory window. arc-rebar writes the card's ReBAR register, then removes and rescans the root port. Intel engineers have proposed a kernel-level fix for this, though it hasn't been merged yet. On a Supermicro X9DRH-7TF with dual Xeon E5-2670 v2 CPUs and a 2015 BIOS, a B580 went from 256 MiB of CPU-visible VRAM to a 16 GiB window covering all 12 GB. Measured VRAM bandwidth jumped from 15 GB/s to 392 GB/s, and a 4K Vulkan blur that used to stall ran at 39 to 50 FPS.Above 4G Decoding is still needed, and the GPU must sit on its own root port. Only Battlemage has been tested, though the developer expects Alchemist to behave the same way. The tool is built for Debian and Ubuntu, so Windows gamers won't benefit, but it could make Arc a viable option for older servers and workstations.