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Drivers & Software

Journeyman III

Performance issues with Smart Memory Access on PCI express 3.0 board

Hi, recently I tried testing Forza Horizon 5 with my new RX 6600 XT, My Ryzen 3600 and my B450 Aorus M board. I was surprised to see massive stuttering when I was running the benchmark. I tried everything to fix, from reinstalling drivers to change the disk where the game was stored. Turns out that, when I disabled Smart Access Memory through BIOS, the stuttering was gone. Those are the comparison images:

You can see the graphics on the right side.

With SAM Enabled:

SAM EnabledSAM Enabled


With SAM Disabled:SAM DisabledSAM Disabled

I don't know if it's the PCIe 3.0 interface combined with the 8x lanes of the RX 6600 XT causing those issues or if it's a bios+chipset problem, or even if it's a problem of the graphics driver. I tested this out with God of War with Vulkan (using DXVK) and it turns out that disabling SAM also helped (I was having some framedrops in the area around the lake, with my gpu not reaching 100%). I hope there's some fix for this, cause I really like to use SAM with no problems, seeing the huge performance boost around there.

12 Replies
Adept I

I have the same issue, stutters, low FPS and low GPU usage on all games when SAM is on and I use Pcie 4.0 ... If I turn it off everything runs butter smooth, if you ever find a solution let me know! I've been looking for it for months now.



Hello i have exactly the same problem , Ryzeon 9 3900X, 32 gb ram crucial (16x2), Radeon RX 6800 all SAM activated, pure UEFI (not csm), nvme storage crucial P5, direct storage fully compatible, windows 11 22h2 and just after a lot of clean install : same problem and only solution diable SAM.

but Why ? because AMD use Amdkmpfg.sys who is and old but updated driver PCI bus low filter. Like any  other "filter" on windows that's make problem everytime.

However, and that's funny, when use the graphics driver  "Basic render display on windows" with SAM  activated, windows detect with no problem the "large memory range" without using these specific low root bus filter "Amdkmpfg.sys". So why amd continue to use these filter with SAM activated if Windows detect natively the sam. But with a basic driver we can't play and use hardware accelerated 3D applications.

please AMD can you change the Architecture from your driver with a better SAM implementation ?

So I make a reply to my reply yes because :

AMD Amdkmpfg.sys has disappear !!! with AMD SAM enabled on radeon driver 23.2 !!! Yes AMD SAM work with the standard "PCI Express root complex" from Microsoft and a lot of stuttering problem has disappear ! thanks for amd to have fix it after 2 months without driver. it's a great news ! 

hey, i dont understand anything. im now on 23.2.1 driver but when i enable SAM gpu usage drops and cpu usage rises so what can i do?


see if you have plugged 2  or 1 cable between your power supply and pci express 8 pin from your graphics card. it's very important to plug 2 indépendant cable between them. and use optimal performance on windows 11 paramètres.



Adept I

I have a solution and it's not the "PCI Bus low filter" Or AMD SAM :

the problem with low fps and stutter : this is only the HPET : High Precision Event Timer from windows which make interrupt all the 1ms/0,5 ms and i have been used from hackers or crackers since 80's (on BIOS) and introduce to windows since Vista.

When you disabled SAM and let it activate stuttering are always present but the stutter are less important. but when you enabled SAM stuttering are a bit long because AMD SAM improve performance and reduce latency so HPET is a problem with modern system (and it's not present with actual UEFI).

I am not an engineer but it's time for windows to disable all legacy BIOS functionality because HPET is a legacy "devices with no driver"




i also have problems with short hangers, but only in three games and that cannot be reproduced but randomly at intervals of minutes and sometimes up to an hour.

After switching from Windows 11 to Windows 10 it became rarer and if I deactivate SAM it is even rarer, almost not at all.

Can this also be related to HPET or rather not?


Hello i think with lot of test since 2 weeks, find the problem :


Resize BAR (SAM) - OFF 
Data link feature exchange - keep ON or OFF

On Windows :
HPET - Keep ON
DNScache service - start - 4 via REGEDIT (OFF)
Sysmain service    - start - 4 via REGEDIT (OFF)
WSearch service   - start - 4 via REGEDIT (OFF)

Optional depend greatly on hardware and memory : Disable swap file


you can forget this : disable only two things : SR IOV and DATA LINK FEATURE EXCHANGE which strangle the PCI Express bandwidth with full use of it.

Adept II

u want pcie 4.0 Mob to that card to get best performance out it if u wanna use SAM

Adept I



OK Guys, i have not SR-IOV, I have data link feature exchange and SAM : resize BAR+Over 4G and i have resolved the latest stuttering issue with this : yes 23.2.1 it's better with not PCI Bus but New world and borderland 3 stuttering. 

With options i have disabled like say my screen capture no more problem ! i can continue with data link OFF for more performance but that's work so... i can stay like this.