Z490 Motherboard Resizable BAR Performance Impact

[S10JlAbraxis]

I have a Gigabyte Z490 Master motherboard and just updated my BIOS to version F20a.  Included in this BIOS release is the option to turn on Resizable BAR.  This option allows the GPU memory direct access to the CPU bypassing the slower system memory and eliminating the current 250MB limit for each memory call from the GPU.  This feature works with the the latest 30xx Nvidia GPUs and the latest AMD GPUs as well (I have an RTX 390).   NVidia has yet to release a driver officially supporting this feature (they plan to) but implementing it in hardware it still provides some benefit even without the specific GPU driver support.  This feature is not limited to Gigabyte and most motherboard brands (MSI, ASUS for sure) have released this feature as part of recent BIOS updates for their Z490 boards.

 

The reason I am posting about this here is because of the impact this enhancement has on BOX.  While frame rates are up slightly (about 3-5%)  the big difference is the complete elimination of all micro stuttering.  When first loading into a mission and looking around the cockpit everything is completely smooth right off the bat.  There is absolutely no micro stuttering over even the largest cities in any map, or anywhere for that matter.  And in general while flying everything seems much smother even though the frame rate is not that different.  Supposedly once NVidia releases driver support the frame rates should go up on average 10 - 12 percent but what really impressed me is the elimination of all micro stuttering.

 

So if you have the right hardware you may want to give this a try.  To turn this option on in the Gigabyte Z490 boards  enable "Above 4G" then set "Resizable BAR" to auto.

 

 

[RAAF492SQNOz_Steve]

Thanks for this posting.

 

I suspect that NVidia will have to release drivers that support it before it actually does anything.

 

I have Resizable Bar enabled on my MSI Z490 and have tested a couple of scenario's that cause motion reprojection to occur with a HP G2 and a RTX 3090

 

i.e. 

1. Set SteamVR resolution to 150%

2. Set MSAA to 2 and SteamVR resolution to 100%

 

Both scenario's still appear to give the same framerates and reprojection figures as I was getting before enabling Re-Bar.

 

Does look like a positive future feature given all that unused VRAM on a RTX 3090.  Fingers crossed that it meets the Hype expectations.

[S10JlAbraxis]

I think you are correct that there is probably no frame rate impact until a driver is released that supports Re-Bar.  I have noticed a very small increase in frame rate but that could be the result of many different things from the updated BIOS to the latest NVidia driver. 

 

However the elimination of all micro stuttering mostly noticeable over cities is real.  In the past when I flew over a large city, particularly on the Bodenplatte map, I would get several micro stutters.  This happened without exception every time I got close to a city.  Now these micro stutters are completely gone which is a fairly dramatic change for me.  I have noticed similar improvements in a few other games as well.  So something is going on with the BIOS update.  Perhaps even without the driver hardware memory access is somehow improved.  I am not a technical expert so all I can do is comment on the results not the cause.  

 

I do not use VR (4K monitor) so maybe that makes a difference.  There are so many variables with different PCs so it is really hard to determine cause.

[RAAF492SQNOz_Steve]

Found an informative article that reports on testing AMD's SAM with a lot of current games. This is AMD's implementation of Resizable BAR.

 

Some games get a good boost while others (most notably for this forum, Microsoft Flight Sim) get a negative performance impact

 

https://www.techspot.com/article/2178-amd-smart-access-memory/

 

I will be interested to see the test results for IL2 once NVidia releases the drivers.

Edited January 11, 2021 by RAAF492SQNOz_Steve
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