7 ms·

> 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

by 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.
- sirn 3y ago
  Modern CPUs have many limits to protect the CPU and later the clock behavior. For example, clock limit, current limit (IccMax, 307A for 13900K), long power limit (PL1, 125W), short power limit (PL2, 253W), transient peak limit (PL3), overcurrent limit (PL4), thermal limit (TjMax, 100c), Fast Throttle threshold (aka Per-Core Thermal Limit, 107c), etc. It also has Voltage/Frequency curves (V/F curve) to map how much voltage needs to drive a certain frequency. Intel 13900K has a fused V/F curve until its maximum Turbo Boost 2.0 (5.5 GHz) in all cores, and two cores at its Thermal Velocity Boost (aka favored cores, 5.8 GHz). How much to boost depends on By Core Turbo Ratio. For stock 13900K, this is 5.8 GHz for 2 cores, and 5.5 GHz for up to 8 cores with E-cores capped at 4.3 GHz. As you may have noticed, the CPU has a very coarse Turbo Ratio beyond the first 2 cores. This is to allow the clock to be regulated by one of the limits rather than a fixed number. In reality, 253W PL2 can sustain around 5.1 GHz all P-cores, and after 56 seconds it will switch to 125W PL1 which should give it around 4.7 GHz-ish (IIRC). This is why when a motherboard manufacturer decides to set PL1=PL2=4096 without touching other limits, it results in a higher number in benchmark. The CPU will consume as much power as it can to boost to 5.5 GHz, until it hits one of the other limits (usually 100c TjMax). This is how we ended up in this mess in the consumer market. Xeon, on the other hand, has a very conservative and granular Turbo Ratio. My Xeon w9-3495x do have a fused All Core Boost that does not exceed PL1 (56 cores 2.9 GHz at 350W), which makes PL2 exist only for AVX512/AVX workload. (Side note: I always think that PL1=PL2=4096W is dumb since performance gain is marginal at best, and always set PL1=PL2=253W in all machines that I assembled. I think even PL1=PL2=125W makes sense for the most usage. I do overclock my Xeon to sustain PL1=PL2=420W though (this is around 3.6 GHz, which is enough to make it faster than 64-cores Threadripper 5995WX))

by scrlk 3y ago

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.

sirn 3y ago
Modern CPUs have many limits to protect the CPU and later the clock behavior. For example, clock limit, current limit (IccMax, 307A for 13900K), long power limit (PL1, 125W), short power limit (PL2, 253W), transient peak limit (PL3), overcurrent limit (PL4), thermal limit (TjMax, 100c), Fast Throttle threshold (aka Per-Core Thermal Limit, 107c), etc. It also has Voltage/Frequency curves (V/F curve) to map how much voltage needs to drive a certain frequency. Intel 13900K has a fused V/F curve until its maximum Turbo Boost 2.0 (5.5 GHz) in all cores, and two cores at its Thermal Velocity Boost (aka favored cores, 5.8 GHz). How much to boost depends on By Core Turbo Ratio. For stock 13900K, this is 5.8 GHz for 2 cores, and 5.5 GHz for up to 8 cores with E-cores capped at 4.3 GHz. As you may have noticed, the CPU has a very coarse Turbo Ratio beyond the first 2 cores. This is to allow the clock to be regulated by one of the limits rather than a fixed number. In reality, 253W PL2 can sustain around 5.1 GHz all P-cores, and after 56 seconds it will switch to 125W PL1 which should give it around 4.7 GHz-ish (IIRC). This is why when a motherboard manufacturer decides to set PL1=PL2=4096 without touching other limits, it results in a higher number in benchmark. The CPU will consume as much power as it can to boost to 5.5 GHz, until it hits one of the other limits (usually 100c TjMax). This is how we ended up in this mess in the consumer market. Xeon, on the other hand, has a very conservative and granular Turbo Ratio. My Xeon w9-3495x do have a fused All Core Boost that does not exceed PL1 (56 cores 2.9 GHz at 350W), which makes PL2 exist only for AVX512/AVX workload. (Side note: I always think that PL1=PL2=4096W is dumb since performance gain is marginal at best, and always set PL1=PL2=253W in all machines that I assembled. I think even PL1=PL2=125W makes sense for the most usage. I do overclock my Xeon to sustain PL1=PL2=420W though (this is around 3.6 GHz, which is enough to make it faster than 64-cores Threadripper 5995WX))