AMD wants to talk to Intel and Nvidia to enable mutual Smart Access Memory support, or Resizable BAR support. This could improve performance for certain games regardless of platform.
AMD’s Radeon group wants to work with Intel to enable Smart Access Memory support on Intel processors, and the Ryzen division is ready to partner with Nvidia to support GeForce graphics. That’s what AMD’s Scott Herkelman of the Graphics Business Unit tells PCWorld . “Talks are underway if they are interested in enabling this functionality for AMD platforms. We are not going to stop them, in fact, I hope they do.” According to Herkelman, there is still work to be done if competitors want to activate this and Intel must, for example, work together with its motherboard partners.
AMD announced Smart Access Memory as a feature of the Radeon RX 6000 graphics cards with GPUs based on the RDNA2 architecture. The functionality allows processors to access a much larger amount of video memory than is possible by default. According to the company, gamers can look forward to a performance improvement of up to 11 percent with the SAM enabled. In the announcement, the company announced that SAM will only work when using a 5000 series Ryzen processor on a 500 series motherboard, in combination with an RX 6000 series video card. In addition, motherboard manufacturers must add the feature via a bios update.
Users who have successfully obtained an RX 6000 card should update their driver to AMD Radeon driver version 20.11.2 or newer. Initially, the ASUS X570 Crosshair VIII Hero had WIFI, ASRock X570 Taichi, Gigabyte Aorus X570 Master and MSI X570 Godlike support, but more motherboards are now being added. For example, MSI has announced that with its latest bios update all 500 series motherboards will support SAM.
Resizable BAR, an old PCIe feature
Users must enable the functionality themselves and motherboard manufacturers do not use the name Smart Access Memory; the functions to be activated can be found in the PCI settings under the names Above 4G Decoding or Above 4G Memory and Resizing BAR or Resizable BAR. It is not surprising that motherboard manufacturers use that name. AMD’s Smart Access Memory is based on the Resizable BAR capacity that has been included in the PCI Express specification since 2008 . AMD already proposed patches for the Linux kernel in 2015 to get support, and Windows has had it in the Windows Display Driver Model since 2017 .
BAR stands for base address register . For a PCIe device with memory, the BARs specify how much memory is to map and each BAR corresponds to an address range that serves as the communication channel to the PCI device. By default, the BARs are limited to 256MB due to compatibility with 32bit operating systems. Until now, workarounds were needed to make the processor use more video memory. Thanks to the Resizable BAR function, the hardware can indicate which part of the memory can be used and thus it is possible to use all the video memory, which AMD does with Smart Access Memory.
In fact, that function has existed for a long time. The fact that AMD is now introducing it has to do with the fact that the company manages the entire necessary chain, from CPU and motherboard to video card, and can use it independently. With the Radeon RX 6000, AMD is once again playing in the ‘enthusiast segment’, so the company is keen to squeeze as much performance as possible from the cards. Another factor is that the AMD 500 series offers PCIe 4.0 and thus enough bandwidth to actually benefit from a direct access to all video memory.
With that you would expect that the combination of a Radeon RX 6000 with a Ryzen 3000 processor on an X570 motherboard will also receive support for SAM, but there are no plans for that, AMD makes clear. The company focuses on the Ryzen 5000. There don’t seem to be any technical obstacles and even motherboards with PCIe 3.0 should be able to get SAM or Resizable BAR support, although it is not clear what the performance gain would be.
Performance gains vary
The performance gain of Smart Access Memory varies a lot per game. AMD itself speaks of 5 percent gain on 4k resolution for Borderlands 3 with SAM enabled, and 11 percent gain on Forza Horizon 4. We saw hardly any gain on Far Cry New Dawn and Shadow of the Tomb Raider and slightly higher performance on Red Dead Redemption and Troy. At Digital Foundry , the use of SAM led to a nice performance gain with Borderlands 3 and Control, but especially at 1080p and not with other games. With Gamers Nexus , both the 6800 and the 6800XT managed to achieve higher fps with Shadow of the Tombraider, both at 1080p and 4k, but with the other games there was no or less difference.
It is also possible that games perform less because of SAM, depending on how the game engines deal with this. AMD has told Gamers Nexus that games showing deterioration will not be able to use SAM and Nvidia has already announced that it will start working with some sort of ‘blacklist’ for games, as soon as Nvidia will introduce its own variant of Resizable BAR. It is not yet known when that will be the case, but Nvidia has already said that it will introduce this support for video cards with Ampere-GPU with a future software update . This contributes to the fact that we will certainly hear more about this technology.