Enable Resizable BAR On Unsupported Motherboards - Hackaday
A new open-source project allows Intel Arc GPUs to achieve full performance on older motherboards that don't support resizable BAR technology.
Recently released on GitHub, the arc-rebar project addresses a significant limitation for users with Intel Arc GPUs on older motherboards. This software enables resizable BAR functionality, which is crucial for optimal GPU performance but often unsupported on legacy hardware.
Resizable base address register (ReBAR) technology allows GPUs to map more of their video RAM into the PC's address space beyond the standard 256 MB. While this feature has been part of the PCIe specification for some time, Intel's Arc GPUs were specifically designed with ReBAR as a core component, making its absence particularly impactful on performance.
Performance Impact
The initramfs-based fix runs before the GPU driver loads, configuring the BAR settings automatically. Testing with an Intel Arc B580 GPU on a 2015-era Intel Xeon motherboard demonstrated dramatic results, increasing bandwidth from a mere 15 GB/s to 392 GB/s.
This one fix can breathe new life into older systems.
Compatibility Requirements
The project requires a Debian or Ubuntu installation and a supported Intel GPU. Unlike AMD and Nvidia GPUs that were developed without ReBAR as a consideration, Intel's newer generations depend on this feature for optimal performance when the PCIe bus is enumerated.
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