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Prime95 has been a bad test for years now. Literally since the introduction of AVX2, it has been known that overclocking and running Prime95 will cause rapid e

by paulmd 7y ago

Prime95 has been a bad test for years now. Literally since the introduction of AVX2, it has been known that overclocking and running Prime95 will cause rapid electromigration and processor degradation on Haswell-E if you attempt to overclock. It's fine for like a few minutes but you should not attempt to do 24 hour Prime95 runs like people used to do, that was in the days before AVX was a thing. https://rog.asus.com/articles/usa/rog-overclocking-guide-core-for-5960x-5930k-5820k/ https://rog.asus.com/articles/usa/rog-overclocking-guide-cor... It also does not test all parts of the processor equally, it really just is slamming the cache and the AVX units. You can be "Prime95 stable" and still crash in other things. It's just not a good test anymore in multiple respects. Same thing for Furmark on GPUs. And nowadays GPUs are actually smart enough to realize they're running a power virus and the power management pulls back the power. So again, it doesn't demonstrate anything. Zen2 is supposed to work the same way, if it realizes you're redlining the chip then it should be clocking down somewhat.

jrockway 7y ago
No sequence of instructions should cause the machine to reboot.
- wtallis 7y ago
  That's an excusable outcome if you're overclocking or otherwise tweaking critical operating parameters beyond their safe default ranges.
- marmaduke 7y ago
  Except the 'reboot' command? I'm always curious how it works.
  - deleted 7y ago
    [deleted]
  - monocasa 7y ago
    Normally you'd ask the chipset so that it can reset all the peripherals at the same time. On Intel you can also intentionally "triple fault" the CPU and that'll cause it to reset. The way that works is you tell the CPU that it doesn't have interrupt handlers anymore, then cause a software interrupt. Then the CPU will first try to call your interrupt handler (but that'll fail because you told it there are no handlers), then errors during an interrupt cause a "double fault" interrupt that's supposed to handle those errors (but once again, there's no handlers), so now you're in a "triple fault" condition and the only way to recover is to reset, so that's what the CPU does.
RobLach 7y ago
That sounds like it’s a great test actually.
- paulmd 7y ago
  What part of damaging your processor due to current draw, while not actually demonstrating any particular level of processor stability, sounds like a great test? Nice contrarianism. Yes, you can run it, and it should run successfully. Yes, sustained testing will rapidly damage your processor and cause notable performance degradation (reduced maximum overclocks/increase in required voltages) within a matter of days, and yes, you can still crash in Aida64 or other stress tests because it's not testing the whole processor very well. It's far outside the normal current draw, even compared to other AVX2 loads like video encoding. It's an AVX load that fits entirely inside instruction cache and will hammer the AVX2 units nonstop at the maximum possible rate with absolutely no other instructions going to any of the other units. That's not how any other workload behaves, even video encoding. CPUs are not designed around that, they're designed for some reasonably normal mix of instructions. Yes, it's a good idea to stress your processor a bit more than normal to prove it's stable, but if you make your 'proof charge' too large you will still damage the firearm.
  - abstractbarista 7y ago
    I don't understand, when I buy a processor I expect it to work 100% load for all of the instruction set. Anything less is a defective product, and should be returned. Furthermore, it should be able to do this 24/7 for years at a time. This test, assuming it actually does kill the processor or stops executing, clearly indicates it should be returned.
    - paulmd 7y ago
      It's fine at normal clocks. Not good for the chip, but it won't kill it within the normal operating lifetime (say, 3-5 years). That's why chips ship with a little more voltage than they need, so that they can suffer some electromigration and still function. Overclocking? Yeah, it'll kill it quick, and that's your problem, because you're operating it outside normal specifications (more voltage than designed). If that's your standard, that you should be able to overclock and then redline the chip 24/7 for an unlimited period of time and it should never kill the chip, then you're going to be disappointed. The fact that Threadripper is having problems is definitely a fault but it's something that you really shouldn't be doing anyway (and it sounds like the problem is the motherboard not the processor). More generally: this is like arguing that you should be able to buy a camry and run redlined 24/7 and get the inevitable engine failures covered by warranty. If the manufacturer finds out you're doing that, they're not going to cover it, because it's not normal usage. Somehow people think it's a reasonable expectation for processors.
mrob 7y ago
"Power virus" is a propaganda term invented by hardware manufacturers as an excuse to avoid fixing their defective hardware.
- paulmd 7y ago
  Designing chips that can be safely run at redline 24/7 will inevitably involve a significant reduction in voltage (and thus clocks) for the 99.99999% of users who aren't running them at redline 24/7. Would you buy a GPU that you could safely run Furmark on 24/7 if it was limited to, half or 3/4 of the clocks? That's basically what you're proposing. I seriously doubt that you would actually lay money down for that shit. The market as a whole certainly wouldn't, they would buy the card that's faster under actual real-world workloads and/or didn't require manual overclocking to achieve its potential in real-world workloads. The good news is that you can have it both ways. Modern power management is smart enough to figure out when you're running a power virus and it will downclock to those safe levels, while us normies can get competitive clocks when running our real-world code. It works pretty well most of the time.
  - theevilsharpie 7y ago
    > Would you buy a GPU that you could safely run Furmark on 24/7 if it was limited to, half or 3/4 of the clocks? Given that modern GPUs have complex frequency scaling algorithms that take temperature and power usage into account when setting clock speed, there's a good chance that a modern GPU will do exactly that. > Modern power management is smart enough to figure out when you're running a power virus and it will downclock to those safe levels, while us normies can get competitive clocks when running our real-world code. Which is perfectly fine, as long as the clock speed behavior is disclosed (which it is). What isn't fine is a product running at such a high speed from the factory that running certain workloads damages it.
    - Filligree 7y ago
      If you look back at the OP, he specified "while overclocking". I believe that's where the issue lays. Overclocking usually also means increasing the voltage.
rasz 7y ago
>electromigration and processor degradation on Haswell-E So what you are really saying is Intel made another defective product.
- paulmd 7y ago
  No, I'm just using that as an officially documented example of Prime95 being problematic. AMD is subject to electromigration as well. I've seen a couple guys on Reddit already degrade their Zen2 chips from pushing 1.4V through them just during normal usage, not even Prime95. Literally weeks of usage. Anti intel circlejerk ahoy.

by paulmd 7y ago

jrockway 7y ago

No sequence of instructions should cause the machine to reboot.

wtallis 7y ago
That's an excusable outcome if you're overclocking or otherwise tweaking critical operating parameters beyond their safe default ranges.
marmaduke 7y ago
Except the 'reboot' command? I'm always curious how it works.
- deleted 7y ago
  [deleted]
- monocasa 7y ago
  Normally you'd ask the chipset so that it can reset all the peripherals at the same time. On Intel you can also intentionally "triple fault" the CPU and that'll cause it to reset. The way that works is you tell the CPU that it doesn't have interrupt handlers anymore, then cause a software interrupt. Then the CPU will first try to call your interrupt handler (but that'll fail because you told it there are no handlers), then errors during an interrupt cause a "double fault" interrupt that's supposed to handle those errors (but once again, there's no handlers), so now you're in a "triple fault" condition and the only way to recover is to reset, so that's what the CPU does.

RobLach 7y ago

That sounds like it’s a great test actually.

paulmd 7y ago
What part of damaging your processor due to current draw, while not actually demonstrating any particular level of processor stability, sounds like a great test? Nice contrarianism. Yes, you can run it, and it should run successfully. Yes, sustained testing will rapidly damage your processor and cause notable performance degradation (reduced maximum overclocks/increase in required voltages) within a matter of days, and yes, you can still crash in Aida64 or other stress tests because it's not testing the whole processor very well. It's far outside the normal current draw, even compared to other AVX2 loads like video encoding. It's an AVX load that fits entirely inside instruction cache and will hammer the AVX2 units nonstop at the maximum possible rate with absolutely no other instructions going to any of the other units. That's not how any other workload behaves, even video encoding. CPUs are not designed around that, they're designed for some reasonably normal mix of instructions. Yes, it's a good idea to stress your processor a bit more than normal to prove it's stable, but if you make your 'proof charge' too large you will still damage the firearm.
- abstractbarista 7y ago
  I don't understand, when I buy a processor I expect it to work 100% load for all of the instruction set. Anything less is a defective product, and should be returned. Furthermore, it should be able to do this 24/7 for years at a time. This test, assuming it actually does kill the processor or stops executing, clearly indicates it should be returned.
  - paulmd 7y ago
    It's fine at normal clocks. Not good for the chip, but it won't kill it within the normal operating lifetime (say, 3-5 years). That's why chips ship with a little more voltage than they need, so that they can suffer some electromigration and still function. Overclocking? Yeah, it'll kill it quick, and that's your problem, because you're operating it outside normal specifications (more voltage than designed). If that's your standard, that you should be able to overclock and then redline the chip 24/7 for an unlimited period of time and it should never kill the chip, then you're going to be disappointed. The fact that Threadripper is having problems is definitely a fault but it's something that you really shouldn't be doing anyway (and it sounds like the problem is the motherboard not the processor). More generally: this is like arguing that you should be able to buy a camry and run redlined 24/7 and get the inevitable engine failures covered by warranty. If the manufacturer finds out you're doing that, they're not going to cover it, because it's not normal usage. Somehow people think it's a reasonable expectation for processors.

mrob 7y ago

"Power virus" is a propaganda term invented by hardware manufacturers as an excuse to avoid fixing their defective hardware.

paulmd 7y ago
Designing chips that can be safely run at redline 24/7 will inevitably involve a significant reduction in voltage (and thus clocks) for the 99.99999% of users who aren't running them at redline 24/7. Would you buy a GPU that you could safely run Furmark on 24/7 if it was limited to, half or 3/4 of the clocks? That's basically what you're proposing. I seriously doubt that you would actually lay money down for that shit. The market as a whole certainly wouldn't, they would buy the card that's faster under actual real-world workloads and/or didn't require manual overclocking to achieve its potential in real-world workloads. The good news is that you can have it both ways. Modern power management is smart enough to figure out when you're running a power virus and it will downclock to those safe levels, while us normies can get competitive clocks when running our real-world code. It works pretty well most of the time.
- theevilsharpie 7y ago
  > Would you buy a GPU that you could safely run Furmark on 24/7 if it was limited to, half or 3/4 of the clocks? Given that modern GPUs have complex frequency scaling algorithms that take temperature and power usage into account when setting clock speed, there's a good chance that a modern GPU will do exactly that. > Modern power management is smart enough to figure out when you're running a power virus and it will downclock to those safe levels, while us normies can get competitive clocks when running our real-world code. Which is perfectly fine, as long as the clock speed behavior is disclosed (which it is). What isn't fine is a product running at such a high speed from the factory that running certain workloads damages it.
  - Filligree 7y ago
    If you look back at the OP, he specified "while overclocking". I believe that's where the issue lays. Overclocking usually also means increasing the voltage.

rasz 7y ago

>electromigration and processor degradation on Haswell-E So what you are really saying is Intel made another defective product.

paulmd 7y ago
No, I'm just using that as an officially documented example of Prime95 being problematic. AMD is subject to electromigration as well. I've seen a couple guys on Reddit already degrade their Zen2 chips from pushing 1.4V through them just during normal usage, not even Prime95. Literally weeks of usage. Anti intel circlejerk ahoy.