Why isn't "Resizable Bar"/SAM supported for the RTX 2000 & Super GPUs?

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by BlindBison, Apr 6, 2021.

  1. artina90

    artina90 Member Guru

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    It's probably a liability issue.
    They fear inexperienced users might brick their cards during the firmware update process.
    They don't want to deal with extra RMAs.
     
  2. Caesar

    Caesar Maha Guru

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    Do not worry..... "take it as a grain of salt...."

    Sooner or later.....this technology.....will phase out....
     
  3. OldManRiver

    OldManRiver Member

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    Except when they do with the DP firmware update for example.
     
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  4. Dagda

    Dagda Master Guru

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    is it really that important? in my case if its actually something that will make my current gpu unusable, then i will just upgrade, if not then if i can still play my games and do my simple video renders then I'm ok without it.
     

  5. dr_rus

    dr_rus Ancient Guru

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    It is not when something is running fully GPU limited. The slower a GPU is the less gains there are from ReBAR. So it makes less sense for <30 series from technical POV but still it would be great if 2070/2080/2080Ti at least got the updates.
     
  6. Dagda

    Dagda Master Guru

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    Hmm yeah, your answer made me actually think this will make a great update for other scenarios appart from gaming, for example the raytracing update un pascal was nice but really useless for gaming purposes since the framerate is super low, but actually helped people that still had render farms using pascal gpu to use optix instead of cuda having better render times and a good denoiser.

    Maybe rbar on 20 and below wouldn't be to bad after all.
     
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  7. BlindBison

    BlindBison Master Guru

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    Unrelated, but nice Avi — haven’t seen Eva for years.
     
  8. Undying

    Undying Ancient Guru

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    Just becouse gpuz reads enabled for the vega does not mean gcn benefit any from it.
     
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  9. cucaulay malkin

    cucaulay malkin Ancient Guru

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    true.
    and you need a whitelist of games in the driver or else you're losing performance as many times as you gain some
     
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  10. Undying

    Undying Ancient Guru

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    Sometimes you loose more than you get. Forza 4 is broken on rx580 and bar enabled.
     

  11. cucaulay malkin

    cucaulay malkin Ancient Guru

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    no it isn't "broken" when you're enabling it on a card that is not supposed to use it.
    broken means it's supposed to work but doesn't.
     
    Last edited: Apr 8, 2021
  12. Kevin Mauro

    Kevin Mauro Master Guru

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    Zen, Zen+ and Zen 2 lack required “math” - full-rate _pdep_u32 (that complete “resize-able bar”) . Intel has been supporting this since Haswell. PDEP/PEXT aka ( _pdep_u32) is 250 times faster in Zen 3 than Zen 2 according to Anandtech.

    • What people refer to when they are enabling it in their BIOS on prior AMD cpus... is that true resizable bar or I’m assuming just it but “not at spec” ? Please correct me ... add to this ...
     
  13. Undying

    Undying Ancient Guru

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    Gpuz, aida64... they all read from the bios and even though it says its enabled (rx580+2700x) its not working really.
     
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  14. DanielRX

    DanielRX Active Member

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    PDEP is a BMI2 instruction (bit manipulation instruction) that mix bits using a mask.

    Zen, Zen+ and Zen2 do have PDEP but it's "microcoded" instead of "hard coded" so it takes a while (like 200+ clock cycles) to be executed, instead of four or so.

    PDEP has no direct (or indirect) relation to PCIe and it's really unclear (and nobody seems to be able to explain why it should be relevant) why it should make SAM impossible (or "slow enough to make it not worth") on Zen/Zen+/Zen2.

    I am not an expert but it's unlikely that this single instruction'execution time will make that much of a difference, and using patch code from Xen (that is a paravirtualization system) doesn't make it more clear.
     
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  15. Kevin Mauro

    Kevin Mauro Master Guru

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    Hey thanks man, much appreciated’

    Perhaps some of those online news’ performative reviews elaborate on that more?

    EDIT: Reddit. I mean here too .. the news section of Gurus3D has stuff about SAM
     
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  16. Astyanax

    Astyanax Ancient Guru

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    PDEP is entirely unrelated to SAM and ReBar,

    https://twitter.com/IanCutress/status/1337423558042120194

    Thanks Ian Cuttress, you mislead the tech community again and nobody reads twitter to know of your retractions.
     
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  17. NEP6XSBW

    NEP6XSBW Active Member

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    Then they should make them available for purchase.
     
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  18. Kevin Mauro

    Kevin Mauro Master Guru

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    Last edited: Apr 13, 2021
  19. @man_daddio

    @man_daddio Member

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    It is very weird in this day and age people just make statements not based in any fact. I highly doubt Nvidia is "keeping" people from updating the RTX 2000 series cards to make them buy 3000 series cards. It is not likely people will upgrade from a 2000 series card to a 3000 yet. Plus you can't even buy 3000 series GPUs in most cases unless you buy from scalpers. Plus as others have said the motherboards and CPU have to also support the feature. I have an RTX 2080ti card with an Intel 7820X CPU. I don't think Intel is even concerned with somehow making RB work with the older CPUS. Nor the motherboard manufacturers on their older boards. It is always possible if people request it enough but most people don't even know about RB/SAM. Maybe AMD fans do as they are more locked into the product. RB is not really that much of a boost. It isn't going to make you a better gamer if you are not a good gamer already. It is good for workstation apps though by looks of what benchmarks I have seen. But gaming? Not so much. Not enough to miss anything.
     
  20. bobblunderton

    bobblunderton Master Guru

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    Even if you had the support for resizable BAR / SAM industry-wide on everything, it's only going to truly be an actual benefit if the hardware was designed with this purpose in mind. Otherwise, it's just adding more VRAM (if you happen to have extra, new games are using up to 8gb sometimes more) to the pool of system RAM and it's not going to give you a speed boost.
    The only time it will give you a speed boost on a PCI-E 4.0 system is when the CPU, Chipset, and normally the GPU are designed for it - in that order of importance. It's possible to do it with less, and it may indeed work, but it won't give you the speed boost unless it was intentionally designed this way.
    The reason it works so well on the 5000-series CPUs from AMD is because they were designed for it with what accounts as hardware short-cuts for a pair (maybe more) of operations, regardless if it's called SAM or not.

    *"short-cut" translates from English to the same as "short-circuit" in some languages, it's not the same in this usage.
    EDIT: Forgot to mention that if you have 8gb or less VRAM, don't even waste your time with ReBAR or SAM. That video ram is needed for games more than anything else. Trying to fit a whole city with any meaningful levels of detail into 8gb is an exercise in slowly going completely insane. So unless you have 12~16gb (or more! lucky you!) of VRAM, the results are very rarely going to be double-digit improvements - though it can happen and does.
    This is the best of my knowledge on it, condensed a bit. If this is wrong in some way, and you can cite your correction, please do so.

    @Astyanax You're 100% right on the 'we don't read Twitter'. I hear about someone reading 'Twitter' and 'Tweeting', and I laugh. Some people on the news try to sound hip, they might as well dance with a pink tutu on. No one cares about Twitter, especially not of someone who hasn't even gotten their grey hair yet.
     
    Last edited: Apr 14, 2021

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