@prazola I finally figured out the actual BAR limit in the BIOS (PciBus DXE) by looking at leaked AMI source code.
The 0x3fffffffe is just below 0x400000000 (16GB) and this makes it disable all BARs over that limit. This explains why 16GB BAR didn’t work no matter what.
I’ll later send a modified BIOS with this fixed. Also did 4GB BAR size work for you ? Because looking at the AMI source code it looks like it’s possibly bugged and 4GB doesn’t work for me.
@prazola if you have time for it test 4GB. Will be able to see if it needs patching then as there are some users of the rebar mod with 4GB cards.
@prazola
Z97Ex9PciBusFix.zip (4.4 MB)
BIOS with PciBusDxe fixed to allow 16GB and larger BARs + fixed PciHostBridge to allow more MMIO space.
Should get 16GB BAR working finally.
Great! I’ll test it in 3 hour.
@prazola Finally it’s working.
Do send a screenshot of large memory in device manager. I want to see how the allocation turned out
If you have time for it you could do some FPS comparisons between on and off. @Romulus_ut3 tried the mod and was able to get a significant FPS boost in Cyberpunk 2077 with just 2GB BAR so with 16GB/full VRAM it should be even bigger.
I’ll make a seperate post on the forum on how to patch PciHostBridge and PciBus to remove the BAR size limitations.
I’ll upload some bench asap. I must check what I have locally to install as my connection is very very slow so new triple A games requires a lot of time to download.
Feedbacks:
RDR2 1440p all maxed out (advanced settings also) with TAA max:
default 81 FPS
rebar 92.2 FPS
Now we need other Haswell owners to step up to the plate and try their hand at modding Resizable Bar support for their system.
Hi everyone,
wow those are awsome findings. I myself am running also a Haswell System with a Gigabyte ga z87ds3h Board. I’ve inserted the rebar dxe and can only use 1GB bar. I would like to have these Features .
I have found another “error” with my board which is about power consumption pkg c states are only used to c2 maybe this is also fixable and plagues prazola’s board?
Greetings
Is 4G decoding enabled ? You should get atleast 2GB if it is
Hi Kuri0, 2gb doesn’t work the biggest is 1gb. Gpuz shows me that “Above 4G Decode” is enabled in Bios but i don’t have the Large Memory area in device manager. I think the error lies in the dsdt and pcihost bridge like in prazola’s bios.
Here is the bios i inserted there your dxe and nvme dxe
nvmerebar.zip (5.8 MB)
Here is my extracted IFR but there is Nothing about 4G Decoding
IFR.zip (86.3 KB)
prazola’s BIOS had 4G Decoding showing but broken ACPI DSDT for it. I don’t know how to patch BIOS if it doesn’t have a 4G Decoding option.
Only patches I know are DSDT fix, 16GB BAR limit removal and currently trying to figure out 4GB on Ivy Bridge (got it to boot but lags for some reason). Another patch that needs to be figured out is some Z170 boards forcing GPU to be in 32-bit region even with 4G Decode on
Ok, yeah makes sense one cannot enable a setting thats not even hidden or implemented.
But what i find is strange that gpuz thinks my bios has it enabled?
GPU-Z reports alot of things wrong. A better way if looking at the address allocated to the GPU in device manager and seeing if it’s a 64 bit address (bigger than 4GB)
I have now dowloaded a variety of gigabyte bioses of different z87 boards i always find “above 4g decoding” with uefi tool but after extration with ifrtool there is nothing.
How do you open .ffs in Ghidra?
You have to open the .efi in it (which is inside the ffs viewable with UEFITool). Also there already is a patch in the Github now to increase MMIO region which can be applied with UEFIPatch
