7 ms·

He's not alone; I've had similar problems with my 3960X. It seems to be a power delivery issue, and fortunately fixable if you disable all spread-spectrum and

He's not alone; I've had similar problems with my 3960X. It seems to be a power delivery issue, and fortunately fixable if you disable all spread-spectrum and VRM power-saving options, but the Zen series seems a tricky beast. I've had machine crashes triggered by using the "wrong" CPU scheduler under Linux. It's amazing, in a horrible way.

xxs 7y ago
That would be a motherboard issue not a CPU one, though. Has anyone attached an oscilloscope?
- franzb 7y ago
  Yes: https://forum.level1techs.com/t/3970x-prime95-stability/153206 https://forum.level1techs.com/t/3970x-prime95-stability/1532...
  - codyb 7y ago
    Great thread thanks for sharing. Really makes you want to order an oscilloscope and some CPUs to putz around with. Everything in computer science is such a rabbit hole, great field to be in.
    - gothroach 7y ago
      If you're interested in a relatively inexpensive oscilloscope to play around with, check out the Rigol 1054Z (or 1074Z Plus if you want MSO capabilities). It's four channels and has more than enough features for playing around with, especially for the price. Using the Riglol website, you can unlock all software options on it, including increasing the bandwidth to 100mHz and the memory to 24MP. It was the first 'real' scope I bought and I still use it a fair amount despite having upgraded to a Rohde and Schwarz MSO model. I've been amazed how much I use an oscilloscope after getting one, from measuring ripple on power supplies to diagnosing serial communication issues.
      - fivesixzero 7y ago
        Thanks for the recommendations! I have a DSLabs DScope (100 MHz, 2-channel FPGA scope) and while it’s handy I’d prefer to have a proper hardware scope someday. Rigol’s scopes look like they nicely fit in between the basic DSO/FPGA stuff and the “proper” 4-5 digit priced test bench gear. Any recommendations for learning resources that could help with understanding DC power supply analysis for non-EE types? While refurbishing laptops and working with microcontrollers I’ve run into some odd things where ruling out transient power supply issues would probably be helpful.
        gothroach 7y ago
        The low end Rigols make good entry-level scopes, and have a surprising amount of capability for the price. As for learning resources, I came across a decent article on the subject when I was starting out (1), and most of the oscilloscope manufacturers have whitepapers on SMPS diagnostics, the Tektronics one I read a while back (2) gave a good overview. A lot of the whitepapers have a manufacturer-specific focus, but they still have good information that can be applied to almost any oscilloscope. If you want to get really into the power supply and do high-side measurements you'll need an isolated differential probe, which can cost as much as an inexpensive oscilloscope, but for DC output measurement you shouldn't need anything special. Current probes are a lot more affordable if you're interested in looking at loads or current fluctuations/harmonics, but that's more useful after you've figured out a bit more what specific properties you're trying to measure. 1: https://www.testandmeasurementtips.com/test-switching-power-supplies/ https://www.testandmeasurementtips.com/test-switching-power-... 2: https://download.tek.com/document/3GW_23612_7.pdf https://download.tek.com/document/3GW_23612_7.pdf Edit: I forgot to mention that the EEVblog forums are a good resource also, but they sometimes aren't as friendly as they could be towards people just starting out.
      - tzs 7y ago
        > Using the Riglol website, you can unlock all software options on it, including increasing the bandwidth to 100mHz and the memory to 24MP. It's interesting how Rigol did the locking of those extra features. The unlock key for a feature set for your scope has to be signed by a Rigol private key using an elliptic curve signature system. But they are only using a 56 bit private key. That was quickly brute forced, and key generators proliferated. They used a good library for the cryptography stuff, and except for the short key seem to have used it well and knew what they were doing. This suggests that the choice of a weak key was deliberate. Each family of scopes has its own private key. As few families came out with new private keys, Rigol continued to use 56 bits. When major firmware upgrades came out in existing families, where they could have easily changed to a longer private key, they kept the same 56 bit that was now widely circulated on the net. It seems pretty clear that they are not interested in stopping people from free unlocking.
  - ComputerGuru 7y ago
    I'm really confused the OP there didn't try a different sTRX4 motherboard.
    - franzb 7y ago
      OP here. I wish I had! Unfortunately that's my work machine and I don't have the time to somehow get my hands on a new fairly rare, very expensive motherboard, disassemble my workstation and rebuild it just to see if my motherboard is the culprit. From the experience of other owners of the 3970X, this problem happens with other TRX40 motherboards.
      - ComputerGuru 7y ago
        Makes sense. I’ve done Amazon Prime and returned it because I consider that a defective mobo and fair game to return in the past.
      - xxs 7y ago
        At least EU Amazon is extremely good about RMAs, e.g. international expresses delivery (next day) even without returning the defective component 1st. Return shipment is also covered, i.e. free for the customer. Dunno, if they'd do that for high priced stuff, though. p.s. lovely/lively oscilloscope shots!
leeter 7y ago
I remember when Buildzoid of AHOC did the mobo breakdowns of the TR4 boards and thinking that while some of the super high end boards were probably good for this sort of beating, the mid and low range might struggle hard with the 64/128 part if it ever came into being (3990X was just a rumor at that time). But it looks like they need more caps to handle the transient response time, and probably also some firmware fixes to slow ramp because I don't think all the SMD caps in the world are going to handle that sort of ramp. It's just not possible to get them close enough to the actual CPU without literally putting them under the IHS.
- franzb 7y ago
  Here's BuildZoid review of the motherboard I'm using (GIGABYTE TRX40 Aorus Xtreme): https://www.youtube.com/watch?v=HMUWzDSAS9c https://www.youtube.com/watch?v=HMUWzDSAS9c A very interesting watch if you're interested in electronics in general and in power delivery in particular (the whole YouTube channel is awesome to be honest).
  - leeter 7y ago
    That was one of the few that I thought could handle the 64/128 part. However look at the output filtering: It's roughly the same if not a cap or two larger as what you'd find on x299... which is a higher voltage and thus has lower amperage requirements. I have yet to find a back of board shot but unless it has a ton of SMD AL-poly caps back there that board would still struggle with the ramp described in the thread. Even then I'm not sure the socket resistance wouldn't cause enough V-droop to cause a crash anyway.
- close04 7y ago
  sTRX4 can take one of three CPUs ranging from 24 to 64 cores. The TRX40 Aorus Xtreme that's mentioned in the thread should be the absolute top of the line even if it was launched before the 64 core monster was available. So I'd expect it to work just fine with the 3970X which is a 32 core part. But I wonder if this is a Gigabyte issue who have a history of playing around with the power delivery and using "fake phases" (to the point where they now have to advertise their boards as having 16 "real phases"). As far as I can tell many (most?) reviewers benchmarked the board with 24 core CPUs and most likely skipped on the power intensive tests.
wtallis 7y ago
"A tricky beast" definitely seems fair. These things have to scale per-core power consumption from ~13W down to ~3W on the fly to stay within their 280W limit. To my knowledge, AMD hasn't implemented any proactive measures that are as severe as Intel's AVX512 strategy, where the instructions get split and handled by the narrower vector units for a surprisingly long time while powering up the full-width vector units (and dropping CPU clocks). This AMD instability is only using AVX2: 256-bit SIMD rather than 512-bit. But spread across so many cores, that's still a lot of FPUs to be lighting up.
- tedunangst 7y ago
  That would suggest the instability might be resolved by adding threads one at a time, but does prime95 have an option like that?
  - franzb 7y ago
    That's an interesting thought!
  - Hello71 7y ago
    you can probably bodge it by running a bunch of copies with limited workers, then run your main copy, then kill the starters. or, you could fiddle with the CPU affinity.
  - Filligree 7y ago
    That's something you can do outside of prime95; the schedutil scheduler does that by default, which I believe is why I had hard crashes with ondemand and not schedutil. (Ok, it actually ramps up frequencies slower rather than lock out cores, but the effect is the same.)
- nottorp 7y ago
  So basically Intel underclocks itself to do the AVX stuff while AMD underclocks itself ... less?
  - 7y ago
wyldfire 7y ago
> fortunately fixable if you disable all spread-spectrum If these are on by default, are they required for FCC certification conformance? Presumably the device has not been EMI/EMC tested in the mode where spread-spectrum was disabled.
- Filligree 7y ago
  They are, but I'm not physically in the USA. At any rate, isn't a computer case basically a Faraday cage? The frequencies are up in the microwave band, so I can't imagine there's much range.
  - wyldfire 7y ago
    > computer case basically a Faraday cage? If it was designed well ;) But that's only effective for addressing radiated emissions, not conducted ones.

xxs 7y ago

That would be a motherboard issue not a CPU one, though. Has anyone attached an oscilloscope?

franzb 7y ago
Yes: https://forum.level1techs.com/t/3970x-prime95-stability/153206 https://forum.level1techs.com/t/3970x-prime95-stability/1532...
- codyb 7y ago
  Great thread thanks for sharing. Really makes you want to order an oscilloscope and some CPUs to putz around with. Everything in computer science is such a rabbit hole, great field to be in.
  - gothroach 7y ago
    If you're interested in a relatively inexpensive oscilloscope to play around with, check out the Rigol 1054Z (or 1074Z Plus if you want MSO capabilities). It's four channels and has more than enough features for playing around with, especially for the price. Using the Riglol website, you can unlock all software options on it, including increasing the bandwidth to 100mHz and the memory to 24MP. It was the first 'real' scope I bought and I still use it a fair amount despite having upgraded to a Rohde and Schwarz MSO model. I've been amazed how much I use an oscilloscope after getting one, from measuring ripple on power supplies to diagnosing serial communication issues.
    - fivesixzero 7y ago
      Thanks for the recommendations! I have a DSLabs DScope (100 MHz, 2-channel FPGA scope) and while it’s handy I’d prefer to have a proper hardware scope someday. Rigol’s scopes look like they nicely fit in between the basic DSO/FPGA stuff and the “proper” 4-5 digit priced test bench gear. Any recommendations for learning resources that could help with understanding DC power supply analysis for non-EE types? While refurbishing laptops and working with microcontrollers I’ve run into some odd things where ruling out transient power supply issues would probably be helpful.
      - gothroach 7y ago
        The low end Rigols make good entry-level scopes, and have a surprising amount of capability for the price. As for learning resources, I came across a decent article on the subject when I was starting out (1), and most of the oscilloscope manufacturers have whitepapers on SMPS diagnostics, the Tektronics one I read a while back (2) gave a good overview. A lot of the whitepapers have a manufacturer-specific focus, but they still have good information that can be applied to almost any oscilloscope. If you want to get really into the power supply and do high-side measurements you'll need an isolated differential probe, which can cost as much as an inexpensive oscilloscope, but for DC output measurement you shouldn't need anything special. Current probes are a lot more affordable if you're interested in looking at loads or current fluctuations/harmonics, but that's more useful after you've figured out a bit more what specific properties you're trying to measure. 1: https://www.testandmeasurementtips.com/test-switching-power-supplies/ https://www.testandmeasurementtips.com/test-switching-power-... 2: https://download.tek.com/document/3GW_23612_7.pdf https://download.tek.com/document/3GW_23612_7.pdf Edit: I forgot to mention that the EEVblog forums are a good resource also, but they sometimes aren't as friendly as they could be towards people just starting out.
    - tzs 7y ago
      > Using the Riglol website, you can unlock all software options on it, including increasing the bandwidth to 100mHz and the memory to 24MP. It's interesting how Rigol did the locking of those extra features. The unlock key for a feature set for your scope has to be signed by a Rigol private key using an elliptic curve signature system. But they are only using a 56 bit private key. That was quickly brute forced, and key generators proliferated. They used a good library for the cryptography stuff, and except for the short key seem to have used it well and knew what they were doing. This suggests that the choice of a weak key was deliberate. Each family of scopes has its own private key. As few families came out with new private keys, Rigol continued to use 56 bits. When major firmware upgrades came out in existing families, where they could have easily changed to a longer private key, they kept the same 56 bit that was now widely circulated on the net. It seems pretty clear that they are not interested in stopping people from free unlocking.
- ComputerGuru 7y ago
  I'm really confused the OP there didn't try a different sTRX4 motherboard.
  - franzb 7y ago
    OP here. I wish I had! Unfortunately that's my work machine and I don't have the time to somehow get my hands on a new fairly rare, very expensive motherboard, disassemble my workstation and rebuild it just to see if my motherboard is the culprit. From the experience of other owners of the 3970X, this problem happens with other TRX40 motherboards.
    - ComputerGuru 7y ago
      Makes sense. I’ve done Amazon Prime and returned it because I consider that a defective mobo and fair game to return in the past.
    - xxs 7y ago
      At least EU Amazon is extremely good about RMAs, e.g. international expresses delivery (next day) even without returning the defective component 1st. Return shipment is also covered, i.e. free for the customer. Dunno, if they'd do that for high priced stuff, though. p.s. lovely/lively oscilloscope shots!

leeter 7y ago

I remember when Buildzoid of AHOC did the mobo breakdowns of the TR4 boards and thinking that while some of the super high end boards were probably good for this sort of beating, the mid and low range might struggle hard with the 64/128 part if it ever came into being (3990X was just a rumor at that time). But it looks like they need more caps to handle the transient response time, and probably also some firmware fixes to slow ramp because I don't think all the SMD caps in the world are going to handle that sort of ramp. It's just not possible to get them close enough to the actual CPU without literally putting them under the IHS.

franzb 7y ago
Here's BuildZoid review of the motherboard I'm using (GIGABYTE TRX40 Aorus Xtreme): https://www.youtube.com/watch?v=HMUWzDSAS9c https://www.youtube.com/watch?v=HMUWzDSAS9c A very interesting watch if you're interested in electronics in general and in power delivery in particular (the whole YouTube channel is awesome to be honest).
- leeter 7y ago
  That was one of the few that I thought could handle the 64/128 part. However look at the output filtering: It's roughly the same if not a cap or two larger as what you'd find on x299... which is a higher voltage and thus has lower amperage requirements. I have yet to find a back of board shot but unless it has a ton of SMD AL-poly caps back there that board would still struggle with the ramp described in the thread. Even then I'm not sure the socket resistance wouldn't cause enough V-droop to cause a crash anyway.
close04 7y ago
sTRX4 can take one of three CPUs ranging from 24 to 64 cores. The TRX40 Aorus Xtreme that's mentioned in the thread should be the absolute top of the line even if it was launched before the 64 core monster was available. So I'd expect it to work just fine with the 3970X which is a 32 core part. But I wonder if this is a Gigabyte issue who have a history of playing around with the power delivery and using "fake phases" (to the point where they now have to advertise their boards as having 16 "real phases"). As far as I can tell many (most?) reviewers benchmarked the board with 24 core CPUs and most likely skipped on the power intensive tests.

wtallis 7y ago

"A tricky beast" definitely seems fair. These things have to scale per-core power consumption from ~13W down to ~3W on the fly to stay within their 280W limit. To my knowledge, AMD hasn't implemented any proactive measures that are as severe as Intel's AVX512 strategy, where the instructions get split and handled by the narrower vector units for a surprisingly long time while powering up the full-width vector units (and dropping CPU clocks). This AMD instability is only using AVX2: 256-bit SIMD rather than 512-bit. But spread across so many cores, that's still a lot of FPUs to be lighting up.

tedunangst 7y ago
That would suggest the instability might be resolved by adding threads one at a time, but does prime95 have an option like that?
- franzb 7y ago
  That's an interesting thought!
- Hello71 7y ago
  you can probably bodge it by running a bunch of copies with limited workers, then run your main copy, then kill the starters. or, you could fiddle with the CPU affinity.
- Filligree 7y ago
  That's something you can do outside of prime95; the schedutil scheduler does that by default, which I believe is why I had hard crashes with ondemand and not schedutil. (Ok, it actually ramps up frequencies slower rather than lock out cores, but the effect is the same.)
nottorp 7y ago
So basically Intel underclocks itself to do the AVX stuff while AMD underclocks itself ... less?
- 7y ago

wyldfire 7y ago

> fortunately fixable if you disable all spread-spectrum If these are on by default, are they required for FCC certification conformance? Presumably the device has not been EMI/EMC tested in the mode where spread-spectrum was disabled.

Filligree 7y ago
They are, but I'm not physically in the USA. At any rate, isn't a computer case basically a Faraday cage? The frequencies are up in the microwave band, so I can't imagine there's much range.
- wyldfire 7y ago
  > computer case basically a Faraday cage? If it was designed well ;) But that's only effective for addressing radiated emissions, not conducted ones.