ReBarUEFI README

The project's README from github.com/xCuri0/ReBarUEFI. As one markdown file: README.md.

ReBarUEFI

GitHub Actions ReBarDxe GitHub Actions ReBarState Downloads

A UEFI DXE driver to enable Resizable BAR on systems which don't support it officially. This provides performance benefits and is even required for Intel Arc GPUs to function optimally.

screenshot showing cpu-z, gpu-z and amd software

If using an NVIDIA Turing GPU (20 or 16 series) see NvStrapsReBar for enabling Resizable BAR on it.

Requirements

Usage

Follow the wiki guide Adding FFS module and continue through the steps. It covers adding the module and the additional modifications needed if required.

Once running the modified firmware make sure that 4G decoding is enabled and CSM is off.

Next run ReBarState which can be found in Releases (if you're on Linux build with CMake) and set the Resizable BAR size. In most cases you should be able to use 32 (unlimited) without issues but you might need to use a smaller BAR size if 32 doesn't work

If Resizable BAR works for you reply to List of working motherboards so I can add it to the list. Most firmware will accept unsigned/patched modules with Secure Boot on so you won't have any problems running certain games.

If you have any issues after enabling Resizable BAR see Common Issues (and fixes)

How it works

The module is added to the UEFI firmware's DXE volume so it gets executed on every boot. The ReBarDxe module replaces the function PreprocessController of PciHostBridgeResourceAllocationProtocol with a function that checks for Resizable BAR capability and then sets it to the size from the ReBarState NVRAM variable after running the original function.

The new PreprocessController function later gets called during PCI enumeration by the PciBus module which will detect the new BAR size and allocate it accordingly.

AliExpress X99 Tutorial by Miyconst

Resizable BAR on LGA 2011-3 X99

Instructions for applying UEFIPatch not included as it isn't required for these X99 motherboards. You can follow them below.

UEFI Patching

Most UEFI firmwares have problems handling 64-bit BARs so several patches were created to fix these issues. You can use UEFIPatch to apply these patches located in the UEFIPatch folder. See wiki page Using UEFIPatch for more information on using UEFIPatch. Make sure to check that pad files aren't changed and if they are use the workaround

Working patches

Build

Use the provided buildffs.py script after cloning inside an edk2 tree to build the DXE driver. ReBarState can be built on Windows or Linux using CMake. See wiki page Building for more information.

FAQ

Will it work on a PCIe Gen2 system ?

Previously it was thought that it won't work on PCIe Gen2 systems but one user had it work with an i5 2500k.

Can I use Resizable BAR on my system without modifying BIOS ?

You can use Linux with 4G Decoding on, recent versions will automatically resize and allocate GPU BARs. If your BIOS doesn't have the 4G decoding option (make sure to check hidden) or DSDT is faulty you can then follow the Arch wiki guide for DSDT modification using modifications from DSDT Patching and boot with pci=realloc in your kernel command line. Currently there is no known method to get it on Windows without BIOS modification

I set an unsupported BAR size and my system won't boot

Clear CMOS and Resizable BAR should be disabled. In some cases it may be necessary to remove the CMOS battery for Resizable BAR to disable.

Will less than optimal BAR sizes still give a performance increase ?

On my system with an i5 3470 and Sapphire Nitro+ RX 580 8GB with Resizable BAR enabled in driver I get an upto 12% FPS increase with 2GB BAR size.

Credit

ReBarUEFI (xCuri0/ReBarUEFI)

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2.6K ·GitHub
ReBarUEFI
What is this?ReBarUEFI is a UEFI DXE driver that enables Resizable BAR on systems whose firmware doesn't support it officially — a free performance boost, mostly noticeable in games.
So do I install this inside Windows, or is it part of the BIOS itself?It lives in your UEFI firmware: the module is added to the DXE volume and runs on every boot. A small companion tool, ReBarState (buildable on Windows or Linux), then sets the BAR size via an NVRAM variable.
How do I get it onto my system?Follow the wiki guide Adding FFS module to inject the driver into your firmware, make sure 4G decoding is on and CSM is off, then run ReBarState from Releases (or build it with CMake) to set the BAR size.
Does my hardware need anything special for this to work?4G Decoding should be enabled — without it you're limited to a 1GB BAR (sometimes 512MB). BIOS support for Large BARs helps too, but UEFIPatch patches exist to fix most issues there.
What happens if I pick a BAR size my system can't handle?The system won't boot. Clear CMOS and Resizable BAR gets disabled — in stubborn cases you may have to physically remove the CMOS battery for it to reset.
Can I get Resizable BAR without flashing a modified BIOS at all?On Linux, with 4G Decoding on, recent versions automatically resize and allocate GPU BARs. On Windows there is currently no known method without BIOS modification.
How much FPS does this actually add?The author measured up to 12% more FPS with a 2GB BAR on an i5-3470 with a Sapphire Nitro+ RX 580 8GB, and even less-than-ideal BAR sizes still gave an increase.
I have an NVIDIA Turing card — does it work for me too?Not with this driver alone: for Turing GPUs (RTX 20 / GTX 16 series) the author points to a separate project, NvStrapsReBar, for enabling Resizable BAR on them.
My PC is old — any chance it works on a PCIe Gen2 board?Surprisingly yes: it was previously thought impossible, but one user got it working on a system with an i5-2500k. UEFIPatch patches also cover MMIO limits on Sandy Bridge through Coffee Lake.
Will Secure Boot block the patched firmware?Usually not — most firmware accepts unsigned or patched modules with Secure Boot on, so you won't have problems running certain games.
What are similar projects?cpu-performance-engineering, open-gpu-kernel-modules, deck-as-controller, OpenCorePkg, NoGraphicsAPI, frank-386, llama.cpp, RingOut
Which topics is it in?uefi, computer-architecture, boot, pc-gaming, driver, x86, amd, cmake, optimization, low-level, firmware, hardware
Creator
xCuri0
Size
0.9 MB
Stars
2.6K
Updated
CommitDec 01Release0.3Mar 02
Age
4y
Commits · 90 Days