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AMD Ryzen 9 7900X Performance With ECC DDR5 Memory

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  • deusexmachina
    replied
    Originally posted by coder View Post
    That's saying a 2-DIMMs per channel (sometimes referred to as a 2DPC configuration) will drop it to 3600 MHz. Since there are two "channels", 2DPC means using a total of 4 DIMMs. So, are you planning on using just two DIMMs in the system or would you populate all four slots?


    Right now, the Kingston DDR5 UDIMMs are available in up to 32 GiB DIMMs. So, the answer is that 64 GiB is the max you can run at 5200 MHz, within spec (i.e. not overclocking).


    Well, the fastest ECC DDR4 UDIMMs are just 3200. So, they're not as fast as DDR5, though a bit lower latency.

    As for reliability, ASRock Rack claims that ECC is fully supported on their AM5 server boards. Supermicro is another option.
    Thank you, that is enough for consideration of doing it despite not seeing it done & verified yet. Need a new system, damn is software getting slow :P

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  • coder
    replied
    Originally posted by deusexmachina View Post
    Thanks; I now see the Kingstons... It is unclear if they work at 5200 or are stuck at ~3600, considering AMD's website says this for Zen 4s:

    Max Memory Speed:
    2x1R - DDR5-5200
    2x2R - DDR5-5200
    4x1R - DDR5-3600
    4x2R - DDR5-3600
    That's saying a 2-DIMMs per channel (sometimes referred to as a 2DPC configuration) will drop it to 3600 MHz. Since there are two "channels", 2DPC means using a total of 4 DIMMs. So, are you planning on using just two DIMMs in the system or would you populate all four slots?

    Originally posted by deusexmachina View Post
    ​Additionally, it isn't clear how much ECC RAM can be used with a Zen 4 before having to reduce the frequency
    Right now, the Kingston DDR5 UDIMMs are available in up to 32 GiB DIMMs. So, the answer is that 64 GiB is the max you can run at 5200 MHz, within spec (i.e. not overclocking).

    Originally posted by deusexmachina View Post
    ​​What I said before it that one might as well use a CPU with ECC DDR4 considering the performance, reliability and price ratio (reliability considering "it hasn't been confirmed/tested" and that isn't my job to do, AMD).​
    Well, the fastest ECC DDR4 UDIMMs are just 3200. So, they're not as fast as DDR5, though a bit lower latency.

    As for reliability, ASRock Rack claims that ECC is fully supported on their AM5 server boards. Supermicro is another option.

    Leave a comment:


  • deusexmachina
    replied
    Originally posted by coder View Post
    Huh?


    Kingston sells ECC DDR5-5600 UDIMMs. Not sure if they're compatible with all motherboards.

    There's also a SK Hynix model, but I can't find anywhere to buy it in the US. Not even on aliexpress.

    Thanks; I now see the Kingstons... It is unclear if they work at 5200 or are stuck at ~3600, considering AMD's website says this for Zen 4s:

    Max Memory Speed:
    2x1R - DDR5-5200
    2x2R - DDR5-5200
    4x1R - DDR5-3600
    4x2R - DDR5-3600

    Additionally, it isn't clear how much ECC RAM can be used with a Zen 4 before having to reduce the frequency to speeds that aren't worth it. What I said before it that one might as well use a CPU with ECC DDR4 considering the performance, reliability and price ratio (reliability considering "it hasn't been confirmed/tested" and that isn't my job to do, AMD).

    Last edited by deusexmachina; 02 January 2024, 08:35 PM.

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  • coder
    replied
    Originally posted by deusexmachina View Post
    So basically we have to stick with CPUs with DDR4 if we want ECC unless we want to pay way more for nothing.
    Huh?

    Originally posted by deusexmachina View Post
    We could have DDR5 with proper ECC running at 5400mhz - and that would make Zen 4 CPUs worth it if you can't justify reducing your data integrity... But no, they purposefully omit such products.
    Kingston sells ECC DDR5-5600 UDIMMs. Not sure if they're compatible with all motherboards.

    There's also a SK Hynix model, but I can't find anywhere to buy it in the US. Not even on aliexpress.

    Leave a comment:


  • deusexmachina
    replied
    So basically we have to stick with CPUs with DDR4 if we want ECC unless we want to pay way more for nothing. Or else the only other option is Threadripper which they ensure has ECC available (but via RDIMMs so you can't use it with reasonably priced CPUs). The amount of time we have to waste on dealing with their marketing scams just to use a computer reliable enough for work to make (and not lose) money is ridiculous.

    We could have DDR5 with proper ECC running at 5400mhz - and that would make Zen 4 CPUs worth it if you can't justify reducing your data integrity... But no, they purposefully omit such products.

    Leave a comment:


  • coder
    replied
    Originally posted by peggyramos
    I am considering going for a system with DDR5 ECC memory and I am unsure which platform works better:

    - Intel: 13900k + Asus W680 ACE + Kingston DDR5-4800 ECC UDIMM
    - AMD: 7900x + X670 / B660 + Kingston DDR5-4800 ECC UDIMM

    Is there a better memory?
    I can only comment on the Intel build, since that's also something I've recently looked at. The Qualified Vendor List on ASUS' website does show 3 SK Hynix DIMMs @ DDR5-5600, but I can't find anywhere to buy them in the USA!

    Note that you'll ideally want dual-rank (sometimes called double-sided) DIMMs, as it can add a couple % of performance vs. single-rank. The downside is they're only available in higher capacities and burn a little more power, but probably just like a couple Watts. Also, try to stick with one DIMM per channel, for the best speed and compatibility.

    Regarding what is available in the US, Kingston makes DDR5-5600 ECC UDIMMs, but their compatibility-checker tool doesn't state they're compatible with the ASUS W680 boards, instead listing only their DDR5-4800 ECC UDIMMs. I haven't found any info on the web indicating people successfully used those DIMMs with that board.

    Originally posted by peggyramos
    Are there any 48GB modules on the market yet?​
    Not ECC UDIMMs, as far as I've seen.

    If you can initially get by with lower quantity, you might try buying 2x 16 GB DDR5-4800 DIMMs, and just plan to replace it with 2x 64 GB DDR5-5600 DIMMs in a year or so. Micron has announced 64 GB UDIMMs (though not said anything about ECC versions, that I've seen). The market for ECC UDIMMs is small and slow to evolve.

    Good luck.

    Leave a comment:


  • coder
    replied
    Originally posted by yump View Post
    It seems to me that memory errors are so rare that it's safe to speculatively assume they never happen, so checking for them can be off the critical path. What is the CPU doing different when ECC is enabled?
    Well, ECC-checking probably adds about a nanosecond of latency or less. So, I'm not sure it's worth the complexity.

    I suppose it's an interesting idea, though. It would mean computations not only become dependent on branch predictions, but also ECC-checks from the last load involved in the data dependencies. However, if the benefit is only like 5 cycles deeper speculation, then I'd say it's not worthwhile.
    Last edited by coder; 16 October 2023, 01:55 AM.

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  • yump
    replied
    Originally posted by coder View Post
    I don't follow this point. For a computing system to be usable, memory errors must be sufficiently rare that they don't occur in code segments and generally don't occur in data that would substantially affect software behavior. By the time you're seeing errors often enough for them to affect something like speculative execution, your machine would be crashing apps and causing kernel panics so often that it'd be effectively unusable.
    That is the point. It seems to me that memory errors are so rare that it's safe to speculatively assume they never happen, so checking for them can be off the critical path. What is the CPU doing different when ECC is enabled?

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  • coder
    replied
    Originally posted by yump View Post
    Yeah, I'm confused that it makes any measurable difference at all.
    I wish we had more visibility into those outliers -- specifically, how much run-to-run variability they have, when you change absolutely nothing. I'm skeptical of anything with more than a 2% deficit for ECC.

    Originally posted by yump View Post
    ECC is a perfect candidate for speculative execution, since errors almost never happen. Logically the CPU should be able to roll along as if everything is correct, and only have to rollback extremely rarely.
    I don't follow this point. For a computing system to be usable, memory errors must be sufficiently rare that they don't occur in code segments and generally don't occur in data that would substantially affect software behavior. By the time you're seeing errors often enough for them to affect something like speculative execution, your machine would be crashing apps and causing kernel panics so often that it'd be effectively unusable.

    Leave a comment:


  • yump
    replied
    Originally posted by coder View Post
    When the CPU is running in ECC mode, the CPU's integrated memory controller performs the ECC checking & computation. That can cost you a couple extra nanoseconds, at most. I'd further speculate that perhaps enabling ECC might disable burst chop, as that's just about the only way I can make sense of the more extreme outliers, assuming those results are stable.
    Yeah, I'm confused that it makes any measurable difference at all. ECC is a perfect candidate for speculative execution, since errors almost never happen. Logically the CPU should be able to roll along as if everything is correct, and only have to rollback extremely rarely.

    Leave a comment:

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