reBAR/ SAM and PCIe/ CPU/ GPU optimisation

[albert]

Well this had me stumped for a few days. Since it is a little complicated and misleading, plus most forums don't really explain it too well. Many people are trying to take advantage of the CPU to GPU transfer optimisations made possible by AMD SAM or nVidia reBAR. And quite frankly the support out there by is OEM's terrible. (MSI have told their forum champions not to help with this, r-soles!!!!) Mainly because there is no single switch to enable this.

I thought I would offer up a a little advice on making Resizable BAR (same for AMD SAM I expect) work for new graphics cards (latest AMD and nVidia ranges).

Chaos level article: https://www.nvidia.com/en-us/geforce/news/geforce-rtx-30-series-resizable-bar-support/
Required if you have Volumes that are still MBR not UEFI: Converting partition table type: https://www.windowscentral.com/how-convert-mbr-disk-gpt-move-bios-uefi-windows-10

Essentially the memory transfer through your PCIe bus is limited in size to small chunks of data. Like any communications system, you get big chunks and little chunks, the former need to be fragmented to make them fit. This resizable BAR option allows for larger amounts of graphic related information to flow makeing the delivery of a smoother gaming experience. It is applicable for some newer games, not so important for older games. Having access to utilise the entire frame buffer allows multiple transfers to happen to to GPU from the drives on your PC and can speed up and improve gaming performance.

This is what they suggest you do to enable this, I have placed my view on the ease of doing this along side each step:

Installation Steps (check the article for screenshots etc.)

To successfully activate Resizable BAR on a desktop PC, please follow these steps in order, referring to the expanded installation instructions below:
1) Confirm you have a compatible CPU & CPU chipset (see list below) - Albert says this is innacurate, as 9th gen Intel and possibly older AMD also can handle this. I proved is because my 9700K is working fine with reBAR enabled.
2) Confirm you have a compatible motherboard (see list below) - Albert says Important to check as it's a show stopper, also BIOS support for 4GB or reBAR (4GB is something to do with mining that I haven't read up on yet).
3) Update your motherboard SBIOS, if required, by installing an update from the manufacturer. Then enable Resizable BAR support in your motherboard’s BIOS interface - See previous line.
4) Update to the latest GeForce Game Ready Driver (version 465.89 WHQL at the time of writing, released March 30th, 2021), or a later version - Obviously.
5) If you have a GeForce RTX 3060, you’re good to go. If you have a GeForce RTX 3060 Ti, 3070, 3080, or 3090, then you may require an updated VBIOS - The OEM of your graphics card will have a new vBIOS which should be installed using their standard method for such things. MSI was finiky, but worked.
6) If you have a Founders Edition graphics card from NVIDIA, get your VBIOS update tool directly from our website. If you have a custom partner card, get the update tool from their site (see list below) - If you went native nVidia, they suppoy a tool just for you (Whitey)
7) Verify Resizable BAR is enabled in the NVIDIA Control Panel (see instructions below) - Well this is also obvious, but there are about 6 things missing between the above line and actually getting here.

Steps They missed:

1) What they forget to mention is that this cannot work on MBR volumes. So you have to convert your boot drive to UEFI, and that can be done safely but is a little scary. Actually why any of us are using MBR in this day and age is another question, for me is't because I never knew any better. I imagine the server and PC guys and gals on the forums will know the answer.
2) Your BIOS will be set to legacy mode by default and after converting the boot drive you need to change this to UEFI. Important: for AMI BIOS this means also changing the Windows 10 WQHL setting. Most BIOSes support dual Legacy and UEFI.
3) Enabling 4GB and reBAR in the BIOS will change a few other things, like memory allocated to your on board graphics card, plus in 2) above, the BIOS should know there are a few things other than reBAR needed to make it work and change them. So it will look like more parts of your BIOS change settings than you really adjusted. I eventually trusted the BIOS. IF you try to guess this part you may have to reset your CMOS, as likely the grphics settings in the BIOS will be messed up. I had to reset twice. Nothing terrible just inconvenient.

I'll stop now since I am tired from typing, but if anyone is trying this and struggling I will happily help.

[albert]

Oh and I don't expect any replies to this but first to do so I will award you a brand new AMD Radeo 6950XT Ti graphics card with 27GB of  DDR7X !! Just PM when you reply so I don't miss the event.

[BrotherTobious]

Good luck with  that  I am sure you will do fine mate

[BrotherTobious]

And very well played

[Whitey]

Thanks Albert, Got mine done tonight and was really painless.  

[albert]

Thanks Albert, Got mine done tonight and was really painless.  

I seem to get about 12fps more in Cyberpunk, and it feels smoother. Of course they just brought out v1.2 so who knows.