Can anyone confirm resizable BAR support for AMD CPUs?

[SamSegal]

Introduction:

Spoiler

Hi all,

I've recently bought the Intel Arc A750 (ASRock challenger OC version) as an upgrade to my GTX 1060.
Painfully enough, despite my thorough research, I failed to notice the intel Arc GPU series heavily relies on resizable bar.

Resizable BAR / re-BAR / Smart Access Memory / Clever Access Memory, from what I gather - allows the CPU to access
the entire memory of the GPU instead of working with chunks of 256MB.

My current setup has a Ryzen 5 2600 and an A320 motherboard. Seems like both on the CPU and the Motherboard,
I am 1 generation short of supporting resizable bar.

Upon testing the Arc A750, I was notified multiple times that re-bar isn't enabled.
Trying a game like Overwatch 2 showed just how impactful it was.
For a CPU as old as mine, the Arc A750 immediately caused a CPU bottleneck (which was at 100%).

And thus, the performance was even worse than the GTX 1060, with noticeable mouse lag inputs, presumably because the PCU was busy trying
to keep up with the GPU and couldn't spare time to handle basic stuff like polling the mouse inputs.

According to this page, Intel states that (some) Ryzen 3000 series CPUs and Ryzen 500 series motherboards support re-bar.
Due to my bad experience in keeping my system upgradable, I wish to buy the cheapest CPU and motherboard combo to support re-bar.

So,

my question is:

Can anyone confirm whether any of the following AMD CPUs support resizable bar:

Ryzen 5 3500, Ryzen 3 3300X, Ryzen 5 4100 (4000 series does not appear on Intel's page for some reason)

I'm thinking of buying one of the three above and pair it with an A520 motherboard, like the GIGABYTE A520M K V2.

Specifically to enable resizable BAR for the Arc A750. If anyone heard of a similar setup working with re-BAR on,
it'll be great to know I can safely upgrade and fully utilize the GPU.

 

[damric]

Did you disable CSM and enable ReBAR in the BIOS? That's the only way you will know.

 

[Ware]

Can anyone confirm whether any of the following AMD CPUs support resizable bar

Originally AMD said "Smart Access Memory technology enablement requires...Ryzen 5000 or 3000 series CPU (excluding the Ryzen 5 3400G and Ryzen 3 3200G)"
I can't confirm support, but I can suggest you check your desired motherboard's BIOS manual for SAM support.

Looking at this Gigabyte A520 BIOS setup guide, I see an option to enable "Above 4G Decode", but no mention or SAM or Resizable BAR.
Good luck!

 

[wNotyarD]

Looking at this Gigabyte A520 BIOS setup guide, I see an option to enable "Above 4G Decode", but no mention or SAM or Resizable BAR.
Good luck!

With my GB X470, the "Re-Size BAR Support" option appears after enabling "Above 4G Decode", just below.

It should work with any Zen 2 and 3 CPU, and may work with Zen+ but people say performance there is sketchy.

 

[SamSegal]

The Gigabye A520M H shows "Add Re-size bar option for AMD Smart Access Memory support" in one of it's BIOS updates (F12).
This is as solid proof as ever that it supports the feature, depending the BIOS was updated -
even though it doesn't explicitly say "Smart Access Memory" or "re-size bar" in it's specifciation / user manual.

My question is more precise: Does it actually work with CPU's like the ones I mentioned? Did anyone ever run an Arc GPU in such (or similar) CPU / Mobo combination?
I'm afraid of making the purchase and then getting the same "this feature is not supported" sort of response..

 

[wNotyarD]

My question is more precise: Does it actually work with CPU's like the ones I mentioned? Did anyone ever run an Arc GPU in such (or similar) CPU / Mobo combination?
I'm afraid of making the purchase and then getting the same "this feature is not supported" sort of response..

Official AMD stance is: Smart Access Memory (SAM, which is just PCIe ReBar with a fancy name) is supported with Ryzen 3000 processors (but not the 3000G APUs) and newer.
So there's no reason at all for an Arc card not to work with such Ryzens if ReBar is enabled.

 

[QuietBob]

AMD site on Smart Access Memory (https://www.amd.com/en/technologies/smart-access-memory) is no more, but luckily it can be viewed in the Wayback Machine.

Smart Access Memory (SAM) technology is compatible with Ryzen 3000 Series CPUs or later (excluding Ryzen 5 3400G and Ryzen 3 3200G CPUs), AMD desktop kits (4800S Series and later), and an AMD 500 Series motherboard or later with the latest BIOS update (based on AGESA 1.1.0.0 or newer).

SAM is compatible with AMD Radeon RX 5000 Series GPUs or later using Adrenalin 20.11.2 or newer.

Personally, I can confirm that it works with the Ryzen 3 3300X. It's a great little CPU, but the availability has always been scarce and so it probably commands a premium in the used market. A Ryzen 5 3600X is a great alternative with two more cores. It was common, and you'll probably find it cheaper than a 3300X.

The Ryzen 5 3500(X) isn't a good choice. With only 6 threads and a lower boost clock it will perform worse than any of the two.

And the Ryzen 3 4100 is even worse. It has the lowest clock of all these and comes with only 4 MB of L3 cache, as opposed to 16 MB.

 

[freeagent]

It's a great little CPU

I was thinking of you during the black friday "sales"

For the first time since Zen 3 dropped I saw your 3300X for a very respectable price.. I almost grabbed it.

But got mad at myself instead for not buying the 5950X. Adult me vs kid me lol..

 

[Dr. Dro]

Resizable BAR/"SmartAccess Memory" support depends on primarily on the motherboard. The Ryzen 3000 and 5000 CPUs will do it, the 4000G/5000G (which includes the 4100 with disabled iGPU) might - no first hand experience here.

To support this, the following options should be enabled on the motherboard:

- Resizable BAR set to "Auto"
- Above 4G Decoding support set to "Enabled"
- CSM set to "Disabled" and OS installed in UEFI mode (it cannot be used in legacy BIOS mode)

Some super low-end motherboards like the one you mentioned might not have these options since they aren't intended for gaming PCs, in which case ReBAR/SAM might not be supported. Chances are good, but I've no first-hand experience with that motherboard and can't guarantee it. An affordable option which does support it and should be within your reach is the AsRock B450M Steel Legend - look at purchasing that instead.

IMO: Ryzen 5 5600 + B450M Steel Legend = solid entry gaming build, relatively affordable, will support this and all other motherboard-level extensions relevant for graphics, making it worth extending your tight budget a little for. Good luck, OP.

 

[SamSegal]

Resizable BAR/"SmartAccess Memory" support depends on primarily on the motherboard. The Ryzen 3000 and 5000 CPUs will do it, the 4000G/5000G (which includes the 4100 with disabled iGPU) might - no first hand experience here.

To support this, the following options should be enabled on the motherboard:

- Resizable BAR set to "Auto"
- Above 4G Decoding support set to "Enabled"
- CSM set to "Disabled" and OS installed in UEFI mode (it cannot be used in legacy BIOS mode)

Some super low-end motherboards like the one you mentioned might not have these options since they aren't intended for gaming PCs, in which case ReBAR/SAM might not be supported. Chances are good, but I've no first-hand experience with that motherboard and can't guarantee it. An affordable option which does support it and should be within your reach is the AsRock B450M Steel Legend - look at purchasing that instead.

IMO: Ryzen 5 5600 + B450M Steel Legend = solid entry gaming build, relatively affordable, will support this and all other motherboard-level extensions relevant for graphics, making it worth extending your tight budget a little for. Good luck, OP.

Thanks for the response The only thing that scares me is that Intel did not mention the 400 series motherboards.
If I understood correctly, both the motherboard and the CPU need to support rebar (i.e, using my current Ryzen 5 2600 the B450 or A520 won't work either).

Then, hopefully re-bar will work with the Arc A750.. I guess if I follow intel's own requierments for the GPU then it should work.

 

[wNotyarD]

Thanks for the response The only thing that scares me is that Intel did not mention the 400 series motherboards.
If I understood correctly, both the motherboard and the CPU need to support rebar (i.e, using my current Ryzen 5 2600 the B450 or A520 won't work either).

Then, hopefully re-bar will work with the Arc A750.. I guess if I follow intel's own requierments for the GPU then it should work.

With the R5-2600 ReBar MAY work, but it's not certain, and certainly more dependant on the motherboard (according to some anecdotal evidence, ASUS and MSI B450/X470 allow it).

 

[_roman_]

With my GB X470, the "Re-Size BAR Support" option appears after enabling "Above 4G Decode", just below.

The MSI B550 Gaming EDGE WIFI had a similar option for a very long time. I think my ryzen 3 3100 with the 6600XT had rbar.

-- I just read a bit all above. Please note - please remember - ASUS and MSI call those uefi option sometimes with another name. Enable it and check it in windows 11 pro than. disable it and check it again in windows 11 pro.

-- I would avoid intel based hardware. I'm affected with a wlan module. Intel needs too much uefi related options enabled / disabled. This should intel communicate more to the end consumer. I was not aware of that fact before purchase of my intel based hardware. (reference: check the news about the intel graphic cards / check the news of today of the intel based processor topic)

-- RBAR is a firmware topic of the mainboard. Than comes the processor. than comes the operating system.

 

[nurgle]

With the R5-2600 ReBar MAY work, but it's not certain, and certainly more dependant on the motherboard (according to some anecdotal evidence, ASUS and MSI B450/X470 allow it).

Used to fully work with my Asus B450 F gaming and a R5 2600. CSM off, above 4G decode on and rebar on

 

[SamSegal]

Used to fully work with my Asus B450 F gaming and a R5 2600. CSM off, above 4G decode on and rebar on

This is exactly what I mean: from Asus website: "Improve ReSizable BAR compatibility for NVIDIA RTX30 series graphics cards"
One of the BIOS updates improved re-bar exclusively for the RTX30 series, is it completely out of the question that Arc A750 might
outright not support re-bar on a B450 motherboard? If the chipset is newer than the requierments page then it makes sense, though -
I doubt AMD releases many AM4 chipsets after 10/16/2023 (last review date for the req page).

Then there's a question of availablity and price. B450 usually go for up to 33% more than the A520, for example.

 

[Solaris17]

This is exactly what I mean: from Asus website: "Improve ReSizable BAR compatibility for NVIDIA RTX30 series graphics cards"
One of the BIOS updates improved re-bar exclusively for the RTX30 series, is it completely out of the question that Arc A750 might
outright not support re-bar on a B450 motherboard? If the chipset is newer than the requierments page then it makes sense, though -
I doubt AMD releases many AM4 chipsets after 10/16/2023 (last review date for the req page).

Then there's a question of availablity and price. B450 usually go for up to 33% more than the A520, for example.

rebar is not an nvidia or AMD invention. it is part of the PCI-E spec.

If you arent willing to make the purchase, and arent willing to test; im not sure what purpose this thread serves. Seems like you are looking for someone to post with the EXACT same system configuration you are wanting to build.

I dont think I am going to let this devolve into tit for tat manu vs manu rebar implementation though.

 

[Dr. Dro]

Thanks for the response The only thing that scares me is that Intel did not mention the 400 series motherboards.
If I understood correctly, both the motherboard and the CPU need to support rebar (i.e, using my current Ryzen 5 2600 the B450 or A520 won't work either).

Then, hopefully re-bar will work with the Arc A750.. I guess if I follow intel's own requierments for the GPU then it should work.

I believe the page you linked in the OP is referring to Intel's own 400 series motherboards (Z490 platforms intended for Intel's 10th Gen CPUs). But that list is not exclusionary, as long as you have a motherboard that supports Resizable BAR functionality and meet the criteria I mentioned in my previous post, it should work even if the CPU is considered unsupported. As @Solaris17 mentioned, it's not a GPU vendor invention but part of the PCI Express standard. So it may work with the R5 2600 if you have a motherboard that will tick all those boxes (CSM off, Above 4G decoding enabled, Resizable BAR: Auto); the AMD B450 chipset (as well as X470) should support the 2600, meaning you probably only need to replace the motherboard if your A320 did not receive a BIOS update that enables this functionality.

Might be worth looking if you haven't already - you could probably get your A750 working without spending a penny. Which motherboard do you have exactly? I might be able to find out if it can do ReBAR or not.

 

[:D:D]

https://www.gigabyte.com/WebPage/785/NVIDIA_resizable_bar.html

TLDR

When Intel says supported it often means validated. So other CPU's might work but haven't been tested by them so don't make the support list.

Example of Rebar using old CPU on legacy BIOS. No UEFI and no BIOS 4G decoding.

Did you now Turin has resizable BAR capability?

I was surprised to learn just recently Turin has resizable BAR capability, so much so that I bought a second hand GTX 1660S to play with. For some reason it's not clear with some other software but if we look under HWiNFO it's well defined. Unfortunately my X99 is out of commission so I'm...

www.techpowerup.com

Above 4G is a permission, not a HW feature. Legacy Video option ROM usually is limited to addresses below 4GiB so large sized BAR's, usually over 1GiB, will not fit below 4GiB. It can be possible to enable CSM and run the graphics UEFI driver to provide frame buffer access to Windows until it loads it's own driver. Not running the UEFI graphics driver means missing out spinning circle and perhaps some messages such as "repairing disk..." while loading Windows.

Having the options in BIOS usually makes life easy otherwise we have to do things ourself including DSDT modification.

Hope that helps.

 

[SamSegal]

rebar is not an nvidia or AMD invention. it is part of the PCI-E spec.

If you arent willing to make the purchase, and arent willing to test; im not sure what purpose this thread serves. Seems like you are looking for someone to post with the EXACT same system configuration you are wanting to build.

I dont think I am going to let this devolve into tit for tat manu vs manu rebar implementation though.

The purpose of this thread is to find out if anyone knows about a similar system (Ryzen 2000 / 3000 (non G) / 4000)
With B400 / B500 / A500 motherboard and have actually seen re-bar supported (not necessarily paired with any GPU,
but that is my end goal here). Doesn't have to be the EXACT same system, would be great if at least either the CPU or the Mobo will be.

I get that re-bar is a PCIe feature, for something rather standard there sure are many names or "flavors" for it and that
got me a bit worried.

For starters, because of the insight I got here - I will first upgrade my motherboard, as rumors of Ryzen 5 2600
supporting re-bar have risen and an emphasize on the motherboard was put, rather than on the CPU.

This thread already helped me, and could potentially help future users which will be in a similar position.

 

[SamSegal]

I believe the page you linked in the OP is referring to Intel's own 400 series motherboards (Z490 platforms intended for Intel's 10th Gen CPUs). But that list is not exclusionary, as long as you have a motherboard that supports Resizable BAR functionality and meet the criteria I mentioned in my previous post, it should work even if the CPU is considered unsupported. As @Solaris17 mentioned, it's not a GPU vendor invention but part of the PCI Express standard. So it may work with the R5 2600 if you have a motherboard that will tick all those boxes (CSM off, Above 4G decoding enabled, Resizable BAR: Auto); the AMD B450 chipset (as well as X470) should support the 2600, meaning you probably only need to replace the motherboard if your A320 did not receive a BIOS update that enables this functionality.

Might be worth looking if you haven't already - you could probably get your A750 working without spending a penny. Which motherboard do you have exactly? I might be able to find out if it can do ReBAR or not.

Hi, thanks for the detailed information!

My motherboard is Gigabyte GA-A320M-S2H (rev. 1.x).
It allows for Above 4G decoding, I disabled CSM but there is no option for Resizable BAR.
I think it runs the latest BIOS version (updated recently), and I can't see any mention of re-bar in the support page.

Today I will buy the Gigabyte A520M H (rev. 1.x) and upgrade it into my current PC.
I will update whether:
1. Resizable BAR is an option in the BIOS
2. Arc A750 will utilize it on this rather outdated, not tested CPU.

 

[Dr. Dro]

Hi, thanks for the detailed information!

My motherboard is Gigabyte GA-A320M-S2H (rev. 1.x).
It allows for Above 4G decoding, I disabled CSM but there is no option for Resizable BAR.
I think it runs the latest BIOS version (updated recently), and I can't see any mention of re-bar in the support page.

Today I will buy the Gigabyte A520M H (rev. 1.x) and upgrade it into my current PC.
I will update whether:
1. Resizable BAR is an option in the BIOS
2. Arc A750 will utilize it on this rather outdated, not tested CPU.

GA-A320M-S2H (rev. 1.x) Support | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ultimate platform fo...

www.gigabyte.com

Try downloading and flashing the latest beta BIOS, version F58d. If current BIOS version is earlier than F32, update to that first and then update to F58d. The option to enable ReBAR might appear.

If it doesn't and you opt to buy a replacement motherboard, don't buy that one. It is likely it will not work with your CPU. The Ryzen 5 2600 is part of the "Pinnacle Ridge" series (Zen 1+), which is unsupported with 500 series chipset (A520, B550, X570)

A520M H (rev. 1.x) Support | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ultimate platform fo...

www.gigabyte.com

You need a 300 or 400 series motherboard, B450 models generally align with price and should offer ReBAR support. B450M Steel Legend I mentioned earlier does support ReBAR, and is generally a solid affordable option. If you mean to stick to Gigabyte, try to get a B450 from them. Perhaps the B450 Aorus Elite if your case can handle full-size ATX instead of just micro? If that's still available, no clue. If you were having reservations on B450 vs. A520 because the 520 is part of 500 series, don't, the B450 is better and unlocked for tweaking. They will also support Zen 3 (including X3D) without any issues, the only restriction that will apply is that you'll be limited to PCI Express Gen 3.

 

[SamSegal]

GA-A320M-S2H (rev. 1.x) Support | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ultimate platform fo...

www.gigabyte.com

Try downloading and flashing the latest beta BIOS, version F58d. If current BIOS version is earlier than F32, update to that first and then update to F58d. The option to enable ReBAR might appear.

If it doesn't and you opt to buy a replacement motherboard, don't buy that one. It is likely it will not work with your CPU. The Ryzen 5 2600 is part of the "Pinnacle Ridge" series (Zen 1+), which is unsupported with 500 series chipset (A520, B550, X570)

A520M H (rev. 1.x) Support | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ultimate platform fo...

www.gigabyte.com

You need a 300 or 400 series motherboard, B450 models generally align with price and should offer ReBAR support. B450M Steel Legend I mentioned earlier does support ReBAR, and is generally a solid affordable option. If you mean to stick to Gigabyte, try to get a B450 from them. Perhaps the B450 Aorus Elite if your case can handle full-size ATX instead of just micro? If that's still available, no clue. If you were having reservations on B450 vs. A520 because the 520 is part of 500 series, don't, the B450 is better and unlocked for tweaking. They will also support Zen 3 (including X3D) without any issues, the only restriction that will apply is that you'll be limited to PCI Express Gen 3.

This is mind blowing, I had no idea the new chipsets dropped support for older CPUs with the same socket...
Then I really am limited only for B450 / X470 if I wish to stick with my 2600.

I guess anything below high end wouldn't be upgradable more than once (The GTX 1060 is actually the 2nd GPU I had on my setup,
prior to that I had a Radeon RX 7770).

Thanks for all of the help! I avoided buying yet another incompatible part for my setup.
I'll most likely go with the Asus Prime B450M-A.

Or shouldn't I?

In it's webpage it states only x8 mode for the x16 PCIe, but the manual states otherwise?

It feels more complicated than it should be..

 

[freeagent]

Wow thats crazy.

I was sure that B550 would support it. Its been awhile since I have used B550 in my main system, but I have a new one on the way to replace one that I killed.

But it does not show Ryzen 2nd gen support anymore

 

[Dr. Dro]

This is mind blowing, I had no idea the new chipsets dropped support for older CPUs with the same socket...
Then I really am limited only for B450 / X470 if I wish to stick with my 2600.

I guess anything below high end wouldn't be upgradable more than once (The GTX 1060 is actually the 2nd GPU I had on my setup,
prior to that I had a Radeon RX 7770).

Thanks for all of the help! I avoided buying yet another incompatible part for my setup.
I'll most likely go with the Asus Prime B450M-A.

Or shouldn't I?
View attachment 376316
In it's webpage it states only x8 mode for the x16 PCIe, but the manual states otherwise?
View attachment 376318
It feels more complicated than it should be..

The manual is a bit out of date but general concept applies, the uppermost PCIe slot is x16, second one is not. Using both drops to x8. Processors with graphics have less PCIe lanes available as integrated graphics take some. This does not apply to your case.

Wow thats crazy.

I was sure that B550 would support it. Its been awhile since I have used B550 in my main system, but I have a new one on the way to replace one that I killed.

But it does not show Ryzen 2nd gen support anymore

Excavator (Bristol Ridge, early AM4 pre-Ryzen APUs) support was removed from all chipsets when AGESA v2 series launched, making the original Ryzen (Summit Ridge) the oldest supported configuration. Then when AMD launched the 500 series chipsets, they removed support for Summit Ridge, Pinnacle Ridge (Zen 1+/Ryzen 2000) and Raven Ridge (early Ryzen APUs, Athlon 200GE).

 

[freeagent]

The manual is a bit out of date but general concept applies, the uppermost PCIe slot is x16, second one is not. Using both drops to x8. Processors with graphics have less PCIe lanes available as integrated graphics take some. This does not apply to your case.



Excavator (Bristol Ridge, early AM4 pre-Ryzen APUs) support was removed from all chipsets when AGESA v2 series launched, making the original Ryzen (Summit Ridge) the oldest supported configuration. Then when AMD launched the 500 series chipsets, they removed support for Summit Ridge, Pinnacle Ridge (Zen 1+/Ryzen 2000) and Raven Ridge (early Ryzen APUs, Athlon 200GE).

I must have been thinking of X570

I am starting to blur the lines in my reality

 

[eidairaman1]

Wow thats crazy.

I was sure that B550 would support it. Its been awhile since I have used B550 in my main system, but I have a new one on the way to replace one that I killed.

But it does not show Ryzen 2nd gen support anymore

B550 steel legend has it