AMD Smart Access Memory / Resizable BAR On Linux Still Ripe For Improvement

[phoronix]

Phoronix: AMD Smart Access Memory / Resizable BAR On Linux Still Ripe For Improvement

Following Mesa 21.0 beginning to see AMD Smart Access Memory optimizations, I ran some benchmarks looking at the current state of S.A.M. / Resizable BAR support on Linux with Radeon graphics...

http://www.phoronix.com/scan.php?page=news_item&px=AMD-Smart-Access-Memory-Initial

[user1]

Apparently, if you have "above 4g decoding" enabled in bios, that means you have resizable BAR support on Linux/AMDGPU. At least with ASUS, not all boards have this BIOS setting. I know that all or most ROG boards have this setting and some Prime boards have it as well, but my board (Prime Z390-P) doesn't have it.

[tajjada]

So, of course AMD lied about "smart access memory" being supported only on the latest generation CPUs and GPUs. Greedy AMD artificially tries to motivate people to buy the latest stuff, by restricting the Windows support.

On Linux we are now adding support and optimizations that are applied regardless of the hardware generation. Older hardware gets a nice performance benefit, too!

[Girolamo_Cavazzoni]

On Linux we are now adding support and optimizations that are applied regardless of the hardware generation.

AMD are doing the optimisations for Linux themselves. Not YOU.

[rene]

So, of course AMD lied about "smart access memory" being supported only on the latest generation CPUs and GPUs. Greedy AMD artificially tries to motivate people to buy the latest stuff, by restricting the Windows support.

On Linux we are now adding support and optimizations that are applied regardless of the hardware generation. Older hardware gets a nice performance benefit, too!

AMD did not lie, they only promised Windows support for that combination. Also, "we" ? You don't sound like a Open Source developer, any patch of yours recently?

[finalzone]

Apparently, if you have "above 4g decoding" enabled in bios, that means you have resizable BAR support on Linux/AMDGPU. At least with ASUS, not all boards have this BIOS setting. I know that all or most ROG boards have this setting and some Prime boards have it as well, but my board (Prime Z390-P) doesn't have it.

I confirm ASUS Prime X570-Pro supports resizable BAR.

[ms178]

So, of course AMD lied about "smart access memory" being supported only on the latest generation CPUs and GPUs. Greedy AMD artificially tries to motivate people to buy the latest stuff, by restricting the Windows support.

On Linux we are now adding support and optimizations that are applied regardless of the hardware generation. Older hardware gets a nice performance benefit, too!

I've asked an AMD developer on the day they announced it here on Phoronix, and he told us an honest answer also that Windows has stricter requirements. You can't blame them for validating that feature on their own hardware and market it that way. I would have chosen a different message and we also might get it enabled on more platforms later on. I've already seen a Vega user who had a 400-series board with the latest BIOS and got a new driver entry with large address space in the device manager. I personally would like to see Windows support on Intel platforms as old as X99 which should be capable to support this, but validation takes some time...

[tajjada]

AMD are doing the optimisations for Linux themselves. Not YOU.

Also, "we" ? You don't sound like a Open Source developer, any patch of yours recently?

Come on guys, seriously? Why the hostility? I said "we" as in the Linux community. We all (Linux users and devs) are getting a nice perf improvement thanks to the Linux drivers not discriminating about hardware support. That "we" never implied me personally taking credit for that specific work. Those drivers, being open-source, are the work of the community (which AMD is a part of, and the biggest contributor to their own drivers), and "we" all get to enjoy it.

Also, yes, BTW, I am an open-source developer. I don't work on the kernel and drivers, though. I contribute to the Bevy rust game engine the related open-source game dev ecosystem.

(as well as working on my own game, but that ain't open-source)

[tajjada]

I've asked an AMD developer on the day they announced it here on Phoronix, and he told us an honest answer also that Windows has stricter requirements. You can't blame them for validating that feature on their own hardware and market it that way. I would have chosen a different message and we also might get it enabled on more platforms later on. I've already seen a Vega user who had a 400-series board with the latest BIOS and got a new driver entry with large address space in the device manager. I personally would like to see Windows support on Intel platforms as old as X99 which should be capable to support this, but validation takes some time...

My point was that in their public announcement to the masses, they made it sound like it was some magical synergy between their latest generation of CPUs and GPUs. That was then quickly debunked, with people showing that it is a standard PCIe feature (which was not really utilized until now) and NV/intel also saying that they will support it.

Of course, the technicalities are more subtle. Linux had support for these PCIe features for a long time. And I don't doubt that technical restrictions on Windows made it difficult.

My point was that the initial mass marketing coming officially from AMD was misleading.And it led to the early announcement-day/launch-day media coverage amplifying that message.

So yes, they lied.

[artivision]

You are a developer so filter you thoughts a little. That is a PCIe future and Intel/NV may support it, doesn't mean that they will gain any performance.