Resizable BAR support

johndoe_36eb90b0

Working together with GPU and mainboard manufacturers, NVIDIA has released drivers with Resizable BAR support.

This feature seems to be supported only on 30x0 RTX series of GPUs, while the mainboard support varies by mainboard vendor.

For more details read the article linked above, but TL;DR version is that it is a free performance upgrade (up to 12% in games, should apply to 3D rendering as well). To enable it you need video BIOS update, mainboard BIOS update, and the latest 465.89 Game Ready drivers (updated Studio Drivers were still not available at the time of this writing).

I have successfully updated BIOS on both my ASUS X299 mainboard and on my MSI VENTUS 3090 RTX and I see the feature reported as enabled in GPU-Z and NVIDIA driver system information page.

Current Studio Drivers (461.92) are presumably unable to take advantage of this hardware feature so I am waiting for updated Studio Driver.

Also, at present it is not clear whether games and applications can take advantage of this without NVIDIA adding explicit support so keep that in mind if you test rendering and you find that there is no benefit.

Richard Haseltine

If I am reading it correctly it relates to transfering data to the GPU - that is not usually a major bottleneck for Iray.

M-C

Richard Haseltine said:

If I am reading it correctly it relates to transfering data to the GPU - that is not usually a major bottleneck for Iray.

Imho this is one of the biggest problems of Iray. Waiting for the Iray preview to kick in while setting up a scene sometimes takes up a lot of time. Especially if you´re doing so several times during the creation process.
So if this new feature helps with that it is very welcome.

johndoe_36eb90b0

Richard Haseltine said:

If I am reading it correctly it relates to transfering data to the GPU - that is not usually a major bottleneck for Iray.

Default CPU "window" into VRAM was limited to 256 MB. All applications transfering large amounts of textures should benefit from this change because now whole VRAM can be mapped and visible to the CPU, and memory transfers can happen in parallel without queuing. Even if it only improves transfer latency that should benefit Iray as well.

TheKD

I was wondering what that BAR was in my bios lol. Never saw anything like that before in a bios so I left it alone. Bummer though, only got a 1070 and 2080 super. Probably be a while before GPU upgrade is doable.

johndoe_36eb90b0

TheKD said:

I was wondering what that BAR was in my bios lol. Never saw anything like that before in a bios so I left it alone. Bummer though, only got a 1070 and 2080 super. Probably be a while before GPU upgrade is doable.

Don't hold your breath when it comes to upgrades -- I paid 1820 EUR for RTX 3090 few months ago when it was released, now it's not available for less than 2930 EUR.

thenoobducky

You can use the gaming driver to test rebar. It has no measurable impact on render performance.* with iray benchmark which admittedly is very low on resource consumption.

prixat

Games are benefitting immediately, since this has been round for more than a decade when Intel/AMD implemented the standard. nVidia are only about 12 years late to the party!

As I understand it, it's about changeable data, when the GPU sends a request it can't handle to the CPU. The CPU does it's calculation and puts the result in the BAR on the GPU, saving the GPU from having to do a fetch from main memory at 'slow motherboard speeds'.

johndoe_36eb90b0

prixat said:

Games are benefitting immediately, since this has been round for more than a decade when Intel/AMD implemented the standard. nVidia are only about 12 years late to the party!

I am not sure it is fair to say that NVIDIA is late because this feature requires more than just driver support. The changes to display driver according to Microsoft are minimal and described here.

Resizable BAR support requires mainboard chipset that supports it, and a mainboard BIOS update to expose the functionality, not to mention video card BIOS update and those are, despite being initially made by NVIDIA, heavily customized and provided by video card vendors.

Furthermore, at least when it comes to Intel, only 4xx, and 5xx series of Intel chipsets are officially supported even though we know that 2xx and 3xx series have the feature as well. What was missing all this time was mainboard BIOS support.

That said, I was lucky with my ASUS PRIME X299-A mainboard since ASUS has released a BIOS update for it and some other older mainboards to enable Resizable BAR despite those boards being old and not being officially supported anymore. Others with older chipsets won't be so lucky.

So please, put the blame where it belongs, or better yet, understand that adding features like this is a complex process that depends on multiple parties doing their part of the effort.