Friday, December 4th 2020

AMD Ryzen 3000 and Older Zen Chips Don't Support SAM Due to Hardware Limitation, Intel Chips Since Haswell Support it

AMD Ryzen 3000 "Matisse" processors based on the "Zen 2" microarchitecture, as well as older AMD processors based on "Zen+" and "Zen" microarchitectures, do not support the company's Smart Access Memory (SAM) feature being introduced with Radeon RX 6000 series graphics cards. SAM is essentially a branding of the Resizable Base-Address Register (Resizable-BAR) feature developed by the PCI-SIG; which enables a processor to see a graphics card's entire video memory as a single addressable block, rather than through 256-megabyte apertures. Apparently the PCI-Express root complex of Ryzen 5000 "Vermeer" processors introduce an instruction called full-rate _pdep_u32/64, which is required for resizable-BAR to work.

It gets more interesting—Intel processors have been supporting this feature since the company's 4th Gen Core "Haswell," which introduced it with its 20-lane PCI-Express gen 3.0 root-complex. This means that every Intel processor dating back to 2014 can technically support Resizable-BAR, and it's just a matter of motherboard vendors releasing UEFI firmware updates for their products (i.e. Intel 8-series chipsets and later). AMD extensively advertises SAM as adding a 1-2% performance boost to Radeon RX 6800 series graphics cards. Since this is a PCI-SIG feature, NVIDIA plans to add support for it on some of its GPUs, too. Meanwhile, in addition to AMD 500-series chipsets, even certain Intel 400-series chipset motherboards started receiving Resizable BAR support through firmware updates.
Sources: CapFrameX (Twitter), flyrobot27 (Reddit), University of Science and Technology of China
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88 Comments on AMD Ryzen 3000 and Older Zen Chips Don't Support SAM Due to Hardware Limitation, Intel Chips Since Haswell Support it

#2
claster17
I thought Zen2 uses the exact same IO die and PCIe controller as Zen3.
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#3
ChosenName
That's a bit embarrassing for AMD - introduce a new performance improving feature; limit it to new GPUs *and* new CPUs; watch the motherboard manufacturers introduce it for existing competitor CPUs....

Hopefully this will be another kick for AMD to "find a way" to introduce SAM on older AMD CPUs that are compatible with the same motherboards that support the latest AMD CPUs.
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#4
Sovsefanden
Haha, thats funny :P However, the performance difference in games (outside of Forza Horizon 4 for some reason) is minimal, I doubt it will matter much..

If old(er) Intel boards requiree UEFI update to support it anyway, how many manufacturers are going to release an UEFI update!? Not many I expect..

QUESTION; If the motherboard does not have SAM enabled, will Nvidia be able to "enable" it thru drivers anyway!?
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#5
Khonjel
Oh come on! Why would you post that? Unless AMD themselves come out and state the reason as such why would you remove the thorn from AMD's bed? Boo!!! bta AMD shill
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#6
Caring1
claster17I thought Zen2 uses the exact same IO die and PCIe controller as Zen3.
That was my thought too.
I'll wait for a correction of the O.P. or myself, preferably the former.
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#8
Xuper
This doesn't matter AMD/Intel support or not. , What matter is How much faster ? according to Anandtech Chart , for PDEP/PEXT in table :
Parallel Bits : Zen 2 = 300 cycle latency , Zen 3 = 3 cycle latency
Deposit/Extreact : Zen2 = 250 cycles per 1 , Zen 3 = 1 cycle latency

This is almost Zen2 is 1% of Zen 3 Performance.How about Intel.Is there any info ?
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#9
Pixrazor
yeah, but how about the gpu side?
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#10
stimpy88
claster17I thought Zen2 uses the exact same IO die and PCIe controller as Zen3.
It does, so it's a marketing lie, or possibly some kind of hardware errata that was corrected... This whole feature is a weird one... Thank AMD for bringing it to light, and thanks to nGreedia for implementing a feature which they would never had released, if it wasn't for AMD...

I wonder how many more features like this, that these companies are sitting on and could implement anytime? I bet Intels little 2-4% perf bumps are nothing more than a microcode update. Shame that there are no tech journalists left to uncover stuff like this anymore.
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#11
_JP_
Still think this is just "we don't want to spend dev time/money on platforms we don't sell anymore" attitude by AMD (motherboard manufacturers might differ, as they usually do), which is neglecting pro bono and kudos points for those still on those platforms and planning upgrades within the same manufacturer. I can make due without SenseMI and StoreMI, but heck, this is a freaking specification standard. Might as well start classifying each manufacturer's uArch with their related implementations like "89% PCI-SIG compatible", like there is for DirectX even though that itself is a mess.
Being a PCI-SIG standard, since PCI-e 3.0 at least, I'm waiting to see Intel's 4600 IGPs all over the place getting a (possible) boost just because of this, while the OG Ryzens sit in the sidewalk. :(
Sovsefanden(outside of Forza Horizon 4 for some reason)
Not really hard to understand when that game had a known and usual development target/focus for a kind of system with a single RAM pool that is accessed by both GPU & CPU (consoles if you haven't guessed it), what differs is how the addressing is made, so if a game were to be ported and then just added the different calls to suit a different type of x86 arch implementation, means the original calls are still there too, unlike other optimizations where those calls might get replaced instead.
Over-simplifying the complex, but I hope it makes sense. :laugh:
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#12
Sykobee
claster17I thought Zen2 uses the exact same IO die and PCIe controller as Zen3.
It could be a PCIe controller firmware difference, even if the die is physically the same.

But in that case, it could be backported, and I'd suggest AMD does that for the good PR.

Still, at least they found an improvement that hadn't been found before, and I can understand only mentioning it for their own CPUs/GPUs for obvious reasons.
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#13
captain_hook
SAM was going to add up to 10%, not 1-2. You mixed up with the "Rage".
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#14
spnidel
now we just have to wait for intel to release BIOS updates to Haswell era motherboards, and everyone can use this feature!

...wait
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#15
Verpal
SovsefandenHaha, thats funny :p However, the performance difference in games (outside of Forza Horizon 4 for some reason) is minimal, I doubt it will matter much..

If old(er) Intel boards requiree UEFI update to support it anyway, how many manufacturers are going to release an UEFI update!? Not many I expect..

QUESTION; If the motherboard does not have SAM enabled, will Nvidia be able to "enable" it thru drivers anyway!?
Unfortunately any PCI related feature are fireware level, driver might be deep into your system, but they are not that deep yet.
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#16
nikoya
next step is for RTX3000 series to support it to get mission complete :)
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#17
thevoiceofreason
claster17I thought Zen2 uses the exact same IO die and PCIe controller as Zen3.
SykobeeIt could be a PCIe controller firmware difference, even if the die is physically the same.
It's not about I/O or PCIe controller, it's a CPU instruction, an ISA extension of the en.wikipedia.org/wiki/Bit_manipulation_instruction_set. In ZEN2 it is apparently emulated in microcode using other instructions which is why it is too slow for any benefit here.
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#18
spnidel
nikoyanext step is for RTX3000 series to support it to get mission complete :)
maybe that was the point? push a new standard like they did with mantle, which evolved into vulkan?
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#19
Julhes
I know what I have to do. Replace my ryzen 3600 with an i5 10600k and z490 motherboard.
I will finally enjoy SAM with my rx6800XT. Thank you AMD for taking your customers for idiots.
Posted on Reply
#20
Caring1
JulhesI know what I have to do. Replace my ryzen 3600 with an i5 10600k and z490 motherboard.
I will finally enjoy SAM with my rx6800XT. Thank you AMD for taking your customers for idiots.
If your buying a new system to spite yourself, why not upgrade to a 5600X and 570? :rolleyes: :kookoo:
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#21
hurakura
So if Intel enable this on latest cpu line amd is fu**ed, no gamer will buy amd. Because Intel is still few % faster in (some) games. And as we know, every % counts
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#22
HansRapad
Caring1If your buying a new system to spite yourself, why not upgrade to a 5600X and 570? :rolleyes: :kookoo:
Simple

That guy probably rocking older board, like x370, and getting 5000 series mean board swap
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#23
laszlo
nikoyanext step is for RTX3000 series to support it to get mission complete :)
as i understand you need a big cache on gpu to can use it so maybe at next generations...
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#25
Outback Bronze
Lucky I've still got a few Haswell chips lying around...
Posted on Reply
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