AMD decided to introduce the ability to utilize Resizable Bar (if you're on the intel platform) or Smart Access Memory aka SAM (if you're on an AMD platform) for their RDNA lineup of graphics card. Initially, only the RX 6000 series of cards were supported, which was later extended to RX 5000 series of cards. While their older range of graphics card like the Radeon VII, VEGA or Polaris didn't support this feature, at least not in official capacity.As with the nature of a community full of enthusiasts, people figured out how to get this feature working on officially unsupported graphics cards from AMD via registry tweaks.
Some Common Misconceptions
A lot of people seem to have all sorts of misconceptions when it comes to this feature, especially when using it on unsupported AMD GPUs. I have seen some absolutely bizarre claims, ranging from:And various other BS claims with no merit to back them up whatsoever.
- SAM aka Smart Access Memory (which is essentially the same thing as Resizable Bar on intel platforms, SAM being a pure marketing label from AMD, just like intel markets SMT as Hyperthreading, thank you 0xCats <3) having "magical(!?) under the hood properties" which makes SAM better than Resizable Bar (yes, your guesses are as good as mine with this one) because AMD's marketing slides said so, aka the "All AMD Advantage"
- REBAR/SAM having no performance effect or even having negative performance scaling when used with unsupported AMD graphics cards (the negative performance scaling is true in some instances even for supported cards too, so...)
- Quoting he said she said driver modder said (and I am very certain said modder didn't say such a thing) that SAM requires a minimum of 8GB of VRAM to activate (!?)
The purpose of this thread is to dispel myths and provide you with directions on how to make Resizable Bar or SAM available on AMD Graphics card that do not officially support it and clarify when and where you can benefit from this and providing you with the options to do this safely, especially those of you who do not wish to install modded drivers. And to top it all, you're going to get some free performance!
Requirements
- A System capable of enabling Resizable Bar,
(If you're on an intel system that doesn't officially support REBAR, not to worry, there is a guide in the making to get this working on those old Ivy Bridge, Haswell, etc. platforms so that they can make use of this too)- The latest AMD GPU drivers,
- A Polaris/VEGA/Radeon VII Graphics card.
The Workaround
It's a very simple fix, basically, AMD's Driver Control Panel changes the values of some registry keys if you have an AMD Graphics card that is capable of utilizing Resizable Bar. But for unsupported Graphics cards, you're going to need to use a "Legacy" setting for you to get the option to toggle it on and off under the performance Tab.To enable Resizable Bar on an unsupported AMD GPU, use this registry file:
If you do not trust a random registry file from an unknown user on the internet, that's okay, here's the code for it so you can verify and create your own registry file to enable this tweak:
Code:
Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{4d36e968-e325-11ce-bfc1-08002be10318}\0000]"KMD_EnableReBarForLegacyASIC"=dword:00000001"KMD_RebarControlMode"=dword:00000001"KMD_RebarControlSupport"=dword:00000001
Simply copy and paste this into a notepad, save the file as a .reg file, open/add it to your current registry and you're set.See AlsoAMD Radeon Resizable BAR / Smart Access Memory Review - 22 Games TestedFaster gaming frame rates for free: Resizable BAR explainedPCI-Express Resizable BAR: RX 6800 XT mithilfe von Intel Core i9-10900K beschleunigtAMD Smart Access Memory (Resizable BAR) Guide | Tech ARPOnce you've done this, simply restarting your PC (in theory, restarting the driver should work too?!) you should see the Resizable Bar/Smart Access Memory option being available and enabled on your unsupported Graphics Card, just like this:
And to disable/revert the changes, use this registry file:
Here's the code for the registry file above so you can verify and create your own version of the registry file to switch REBAR OFF:Code:
Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{4d36e968-e325-11ce-bfc1-08002be10318}\0000]"KMD_EnableReBarForLegacyASIC"=-"KMD_RebarControlMode"=dword:00000000"KMD_RebarControlSupport"=dword:00000000Performance: What to expect?
Enabling this option won't magically turn your Polaris, VEGA or Radeon VII GPU as good as their newer counterparts, however, Resizable Bar/SAM will help you in games where you're CPU bound. Here's an example:Game Title: Cyberpunk 2077
Settings used:
The footage you see was captured using FSR 2.1 mod, with the preset set to "Quality" but you can get gains even when using native resolution. One thing that I noted is that using ReLive to capture footage while ReBar is on causes a performance hit, which doesn't seem to happen with ReBar set to off. But that's probably due to the GPU being more taxed while ReBar is enabled and has no processing power to spare for the additional video encoding workload. When not capturing gameplay using ReLive, the performance figures from having Rebar On is actually slightly higher (51~52 FPS) at this very exact spot.Here are some native resolution comparisons:
Resizable Bar On:
Not all games will show gains from having this enabled on these GPUs, in fact there are games where you won't see any gains at all, or you can come across negative scaling too, and a lot will depend on your system's specs. If you've a really fast CPU and an older GPU, chances are you're already GPU bound in most newer titles, and therefore you may not see a lot of gains.
Resizable Bar Off:
But those of you who are using the likes of the RX 400/500, VEGA or the Radeon VII range of cards on older CPUs like Ivy Bridge, Haswell, or Ryzen Zen1/Zen2 can benefit from this.
You're essentially gaining free performance with this registry tweak, and if you do come across some sort of stability issue, you can simply disable it. There's no harm in trying this out.
Credits:
- The Amernime Modded driver author(s)/team for directing me towards the registry. I couldn't have gotten the Legacy mode working without them.
- @Kuri0 for helping me enable Resizable Bar on my potato home rig with his brilliant REBAR DXE solution.
- And some random naysayers on various discord servers/tech forums, who served as the motivation for creating this thread.
I'll update this thread with more benchmarks/numbers and of course, your feedback will be very much appreciated. Thank you and have a nice day.
chispy, Riekopo, eddieobscurant and 19 others like this.
