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> "Intel's default maximum TDP for the 13900K is 253 watts, though it can easily consume 300 watts or more when given a higher power limit. In our testing, manu

by scrlk 3y ago

> "Intel's default maximum TDP for the 13900K is 253 watts, though it can easily consume 300 watts or more when given a higher power limit. In our testing, manually setting the power limit to 275–300 watts and the amperage limit to 350A, proved to be perfectly stable for our 13900K. That required going into the advanced CPU settings in the BIOS to change the PL1/PL2 limits — called short and long duration power limits in our particular case. The motherboard's default "Auto" power and current limits meanwhile created instability issues — which correspond to a power limit of 4,096 watts and 4,096 amps." [0] The motherboard manufacturers are setting default/auto power and current limits that are way outside of Intel's specs (253 W, 307 A) [1]. [0] https://www.tomshardware.com/pc-components/cpus/is-your-intel-core-i9-13900k-crashing-in-games-your-motherboard-bios-settings-may-be-to-blame-other-high-end-intel-cpus-also-affected https://www.tomshardware.com/pc-components/cpus/is-your-inte... [1] https://www.intel.com/content/www/us/en/content-details/743844/13th-generation-intel-core-and-intel-core-14th-generation-processors-datasheet-volume-1-of-2.html https://www.intel.com/content/www/us/en/content-details/7438... (see pg. 98 and 184, the 13900K/14900K is 8P + 16E 125 W)

eqvinox 3y ago
Your [0] also says: > It's not exactly clear why the 13900K suffers from these instability problems, and how exactly downclocking, lowering the power/current limits, and undervolting prevent further crashes. Clearly, something is going wrong with some CPUs. Are they "defective" or merely not capable of running the out of spec settings used by many motherboards?
- scrlk 3y ago
  > Are they "defective" or merely not capable of running the out of spec settings used by many motherboards? I'd wager good money on the latter. Why would Intel validate their CPUs against power and current limits that are outside of spec? The users reporting issues probably have CPUs that just made it in to the performance envelope to be binned as a 13900K, so running out of spec settings on these weaker chips results in instability. It's cases like this where I wish Intel didn't exit the motherboard space, they were known to be reliable but typically at the cost of having a more limited feature set.
  - RetroTechie 3y ago
    > I'd wager good money on the latter. Don't guess, measure! The proper action here would be to change BIOS settings from their default / "auto" settings to per-Intel-spec safe ones. Same for RAM, and on systems with known good power supplies, CPU cooling, software installs etc. Then one of the following will happen: a) BIOS ignores user settings & problem persists. b) BIOS applies user settings & problem goes away. c) BIOS applies user settings but problem persists. Cases a & b count as "faulty BIOS" (motherboard manufacturer caused). Case c counts as "faulty CPU", and replacement cpu may or may not fix that. No need to guess. Just do the legwork on systems where problem occurs & power supply, RAM, CPU cooling & OS install can be ruled out. Sadly, no doubt there's many systems out there where that last condition doesn't hold.
    - vdaea 3y ago
      I have a 13900K. The default BIOS settings set a maximum wattage of 4096W (!!!) that makes Prime95 fail. If I change the settings back to 253W, what Intel says is the maximum wattage, Prime95 stops failing. Still, I don't know if I should RMA. I got the K version because I intended to overclock in the future. And all of this sounds like I won't be able to. I think increasing the voltage a little bit makes the system more stable. I have to play with it. (Really, if someone can say whether I should RMA or not, I would appreciate some input) Edit: decided to RMA. I have no patience for a CPU that cost me +600€
  - eqvinox 3y ago
    > I'd wager good money on the latter. I don't disagree, but I'm cautious about making a call with the current information available. For example: yes, a "4096W / 4096A" power limit sounds odd, but it's not an automatic conclusion that this limit is intended to work to protect the CPU. Instead, it is a function that allows building a system with a particular PSU dimension — it would be odd if that were overloaded to protect the chip itself. Maybe it is, maybe it isn't. It's also very much possible that the M/B vendors altered other defaults, but… I don't see information/confirmation on that yet. It used to be that at least one of the settings is the original CPU vendor default, but last I looked at these things was >5 years ago :(. > It's cases like this where I wish Intel didn't exit the motherboard space, Full ACK.
mschuster91 3y ago
> amperage limit to 350A Jesus. By German electrical code, you need a 70 mm² cross-section of copper to transfer that kind of current without the cable heating up to a point that it endangers the insulation. How do mainboard manufacturers supply that kind of current without resistive loss from the traces frying everything?
- bonzini 3y ago
  Those electrical code cross sections are for 350A at 230V, corresponding to about 80 kW (400V is the same as it's actually three 230V wires). Processors operate at about 1V. At 300W it's enough to use a much smaller cross section, which is split across many traces.
  - coryrc 3y ago
    That's not how I^2R losses work. Voltage is not relevant.
    - planede 3y ago
      I agree. However voltage is relevant for insulation, which also affects how heat can dissipate for the wire, and might also be relevant for a failing wire, when higher and higher voltage can build up at the point of failure (not sure if it's a common engineering consideration outside of fuses, which are designed to fail).
    - bonzini 3y ago
      At 300W there's only so much power that can become heat. With 80 kW flowing through the wire, if the insulation melts due to excessive wire resistance you call the fire brigade.
- coryrc 3y ago
  That code is for round wire (minimal surface area per volume) that can be placed inside insulation in walls. This 350A is flat conductors (maximal surface area thus heat dissipation) and very short (not that much power to dissipate so the things it connects to have a significant effect on heat dissipation).
michaelt 3y ago
> The motherboard manufacturers are setting default/auto power and current limits that are way outside of Intel's specs The CPU only draws as much power as it needs, though? I mean, if you plug a 20 watt phone into a 60 watt USB-C power supply, or a 60 watt laptop into a 100 watt USB-C power supply the device doesn't get overloaded with power. It draws no more current than it needs. The motherboard's power limits should state the amount of power the PCB traces and buck regulators are rated to provide to the socket - and if that's more than the processor needs that's good, as it avoids throttling.
- rfoo 3y ago
  The problem is these processors are unstable if they are not properly throttled. Of course users, especially enthusiast motherboard consumers, hate throttling, hence the default.
- scrlk 3y ago
  * User is running a demanding application (e.g. game). * CPU clock speed increases (turbo boost), as long as the CPU isn't hitting: 1) Tj_MAX (max temp before thermal throttling kicks in); 2) the power and current limits specified by the motherboard (in this case, effectively disabled by the out of spec settings). * Weaker chips will require more power to hit or maintain a given turbo clock speed: with the power and current limits disabled, the CPU will attempt to draw out of spec power & current, causing issues for the on die fully-integrated voltage regulator (noting that there's also performance/quality variance for the FIVR), resulting in the user experiencing instability.
wongarsu 3y ago
Drawing peak power far in excess of the TDP is what all Intel processors have been designed to do for many years now. Some consider it cheating the benchmarks, but the justification is that TDP is the Thermal Design Power. It's about the cooling system you need, not the power delivery. If you make reasonable assumptions about the thermal inertia of the cooling system you can Turbo Boost at higher power and hope the workload is over before you are forced to throttle down again. Any mainboard that sets power limits to the TDP would be considered wrong by both the community and Intel. This looks like a solid indication that the issue is with Intel

by scrlk 3y ago

eqvinox 3y ago

Your [0] also says: > It's not exactly clear why the 13900K suffers from these instability problems, and how exactly downclocking, lowering the power/current limits, and undervolting prevent further crashes. Clearly, something is going wrong with some CPUs. Are they "defective" or merely not capable of running the out of spec settings used by many motherboards?

scrlk 3y ago
> Are they "defective" or merely not capable of running the out of spec settings used by many motherboards? I'd wager good money on the latter. Why would Intel validate their CPUs against power and current limits that are outside of spec? The users reporting issues probably have CPUs that just made it in to the performance envelope to be binned as a 13900K, so running out of spec settings on these weaker chips results in instability. It's cases like this where I wish Intel didn't exit the motherboard space, they were known to be reliable but typically at the cost of having a more limited feature set.
- RetroTechie 3y ago
  > I'd wager good money on the latter. Don't guess, measure! The proper action here would be to change BIOS settings from their default / "auto" settings to per-Intel-spec safe ones. Same for RAM, and on systems with known good power supplies, CPU cooling, software installs etc. Then one of the following will happen: a) BIOS ignores user settings & problem persists. b) BIOS applies user settings & problem goes away. c) BIOS applies user settings but problem persists. Cases a & b count as "faulty BIOS" (motherboard manufacturer caused). Case c counts as "faulty CPU", and replacement cpu may or may not fix that. No need to guess. Just do the legwork on systems where problem occurs & power supply, RAM, CPU cooling & OS install can be ruled out. Sadly, no doubt there's many systems out there where that last condition doesn't hold.
  - vdaea 3y ago
    I have a 13900K. The default BIOS settings set a maximum wattage of 4096W (!!!) that makes Prime95 fail. If I change the settings back to 253W, what Intel says is the maximum wattage, Prime95 stops failing. Still, I don't know if I should RMA. I got the K version because I intended to overclock in the future. And all of this sounds like I won't be able to. I think increasing the voltage a little bit makes the system more stable. I have to play with it. (Really, if someone can say whether I should RMA or not, I would appreciate some input) Edit: decided to RMA. I have no patience for a CPU that cost me +600€
- eqvinox 3y ago
  > I'd wager good money on the latter. I don't disagree, but I'm cautious about making a call with the current information available. For example: yes, a "4096W / 4096A" power limit sounds odd, but it's not an automatic conclusion that this limit is intended to work to protect the CPU. Instead, it is a function that allows building a system with a particular PSU dimension — it would be odd if that were overloaded to protect the chip itself. Maybe it is, maybe it isn't. It's also very much possible that the M/B vendors altered other defaults, but… I don't see information/confirmation on that yet. It used to be that at least one of the settings is the original CPU vendor default, but last I looked at these things was >5 years ago :(. > It's cases like this where I wish Intel didn't exit the motherboard space, Full ACK.

mschuster91 3y ago

> amperage limit to 350A Jesus. By German electrical code, you need a 70 mm² cross-section of copper to transfer that kind of current without the cable heating up to a point that it endangers the insulation. How do mainboard manufacturers supply that kind of current without resistive loss from the traces frying everything?

bonzini 3y ago
Those electrical code cross sections are for 350A at 230V, corresponding to about 80 kW (400V is the same as it's actually three 230V wires). Processors operate at about 1V. At 300W it's enough to use a much smaller cross section, which is split across many traces.
- coryrc 3y ago
  That's not how I^2R losses work. Voltage is not relevant.
  - planede 3y ago
    I agree. However voltage is relevant for insulation, which also affects how heat can dissipate for the wire, and might also be relevant for a failing wire, when higher and higher voltage can build up at the point of failure (not sure if it's a common engineering consideration outside of fuses, which are designed to fail).
  - bonzini 3y ago
    At 300W there's only so much power that can become heat. With 80 kW flowing through the wire, if the insulation melts due to excessive wire resistance you call the fire brigade.
coryrc 3y ago
That code is for round wire (minimal surface area per volume) that can be placed inside insulation in walls. This 350A is flat conductors (maximal surface area thus heat dissipation) and very short (not that much power to dissipate so the things it connects to have a significant effect on heat dissipation).

michaelt 3y ago

> The motherboard manufacturers are setting default/auto power and current limits that are way outside of Intel's specs The CPU only draws as much power as it needs, though? I mean, if you plug a 20 watt phone into a 60 watt USB-C power supply, or a 60 watt laptop into a 100 watt USB-C power supply the device doesn't get overloaded with power. It draws no more current than it needs. The motherboard's power limits should state the amount of power the PCB traces and buck regulators are rated to provide to the socket - and if that's more than the processor needs that's good, as it avoids throttling.

rfoo 3y ago
The problem is these processors are unstable if they are not properly throttled. Of course users, especially enthusiast motherboard consumers, hate throttling, hence the default.
scrlk 3y ago
* User is running a demanding application (e.g. game). * CPU clock speed increases (turbo boost), as long as the CPU isn't hitting: 1) Tj_MAX (max temp before thermal throttling kicks in); 2) the power and current limits specified by the motherboard (in this case, effectively disabled by the out of spec settings). * Weaker chips will require more power to hit or maintain a given turbo clock speed: with the power and current limits disabled, the CPU will attempt to draw out of spec power & current, causing issues for the on die fully-integrated voltage regulator (noting that there's also performance/quality variance for the FIVR), resulting in the user experiencing instability.

wongarsu 3y ago

Drawing peak power far in excess of the TDP is what all Intel processors have been designed to do for many years now. Some consider it cheating the benchmarks, but the justification is that TDP is the Thermal Design Power. It's about the cooling system you need, not the power delivery. If you make reasonable assumptions about the thermal inertia of the cooling system you can Turbo Boost at higher power and hope the workload is over before you are forced to throttle down again. Any mainboard that sets power limits to the TDP would be considered wrong by both the community and Intel. This looks like a solid indication that the issue is with Intel