5 ms·

I don't get it. If it has an all-core frequency of 5GHz, doesn't that mean they've left some single-core boost on the table? Or have they hit some other limit

I don't get it. If it has an all-core frequency of 5GHz, doesn't that mean they've left some single-core boost on the table? Or have they hit some other limit and this part is basically free of thermal limits?

pitaj 7y ago
Yeah it's weird. Why not set the single-core turbo higher?
- deleted 7y ago
  [deleted]
- dual_basis 7y ago
  Marketing.
gchamonlive 7y ago
I believe Intel processors can't boost all cores. At least some tests I have done with my notebook processor (i7 8550u - 4c8t) with `stress -c n`, being n the number of processors, show that for n > 1 the processor doesn't reach 4ghz, only about 3.7ghz, while the package temps are still at around 70 °C. Only a single core on full load reaches 4ghz before throttling.
- shereadsthenews 7y ago
  Yes, there's a table in the firmware that can tell you the maximum speed with N active cores. This one though has the same speed for all values of N.
- clarry 7y ago
  > I believe Intel processors can't boost all cores. And that's exactly what shereadsthenews's point is. They can't boost all cores, and they are not boosting any core beyond the all-core capacity if it's truly a CPU that runs at 5 GHz all the time.
  - XMPPwocky 7y ago
    Turbo Boost can certainly apply to all cores- the limits you hit are TDP and time based, there, not strictly thermal. So, for example, my old laptop CPU would clock itself up to 2.7GHz on all cores... well, okay, it was a dual core, so that's not saying much, but still. But it'd only maintain that boost for a few seconds- under sustained load it dropped down to 2.5. This wasn't because of thermals, but rather because 2.7GHz was a Turbo Boost frequency, and once the PPL timer runs out...
    - XMPPwocky 7y ago
      And to explain why they don't have, say, one core boost to 5.1GHz...well, let's see what siliconlottery says. > As of 3/16/19, the top 38% of tested 9900Ks were able to hit 5.0GHz or greater. > As of 3/16/19, the top 8% of tested 9900Ks were able to hit 5.1GHz or greater. So, Intel'd cut their yield by more than a factor of four if they only let parts that could hit 5.1 into this bin. For a 2% single-core performance boost...
      - mackal 7y ago
        I think those numbers are for chips that can 5.1 GHz all core though, which is probably a lot less than 5.1 GHz single core.
        XMPPwocky 7y ago
        As far as I know, K-series parts don't support binning of individual cores- if you have one bad core that'll only hit 5.0, 1-core turbo to 5.1 will still result in the OS scheduler periodically picking that core to use, it clocking up to 5.1, and problems resulting. Might be wrong, though.
        wtallis 7y ago
        Intel's Turbo Boost 3.0 [1] was their attempt to take advantage of the fact that some cores on a chip can clock higher than others. It does not work well in practice, because it requires too much collaboration with motherboard and OS vendors. This feature is not available on their desktop platform, which the i9-9900KS uses. [1] https://www.intel.com/content/www/us/en/architecture-and-technology/turbo-boost/turbo-boost-max-technology.html https://www.intel.com/content/www/us/en/architecture-and-tec...
- rzzzt 7y ago
  XTU allows setting different turbo multipliers for 1-4 active cores (but the difference from the nominal clock speed typically gets smaller as more cores become active).
- mackal 7y ago
  This is entirely configurable. They generally don't do all core == max boost for power consumption reasons (and I assume yield would be pretty low on chips that can do this) Desktop chips also generally don't have any AVX offset, which is almost always required for 5 GHz all core.
adamparsons 7y ago
I’d guess that the upper limit is stability rather than thermal capacity at that point
- kzrdude 7y ago
  What does stability mean, a bit more exactly? Just curious
  - saltyshake 7y ago
    The CPU not losing its marbles when overclocked. https://devblogs.microsoft.com/oldnewthing/20050412-47/?p=35923 https://devblogs.microsoft.com/oldnewthing/20050412-47/?p=35...
  - bayindirh 7y ago
    The switching speed of silicon has also some upper limit. When you drive silicon faster, it starts to make mistakes. i.e. not all electrons go the where you want them to go. This causes soft-faults and CPU re-executes the part at best, or gives you a BSOD, oops or panic at worst. This upper limit depends on process, layout, power design and power limits of the CPU. Last but, not the least, not all CPUs are created equal on a wafer. I came from an era where we hunted plain blue AMD Athlon dies for higher overclocking potential, since they were from center of the wafer and they were more stable under high load/voltage/clock. I had a 2200MHz Athon (200 x 11) which was faster then AMD's own 2200MHz Athlons, since AMD wasnt offering a 200MHz bus version of their 2200MHz parts.
    - koala_man 7y ago
      >gives you a BSOD, oops or panic at worst. That's not too bad. I'd be much more worried about code silently doing the wrong thing .
      - bayindirh 7y ago
        That's also possible. That's why overclockers run Prime95 to test their CPU stability. Also, a BSOD or panic in the wrong time can cause massive data loss. That's beyond bad sometimes. Edit: I mixed Prime95 with SuperPi. Thanks AaronFriel.
deleted 7y ago
[deleted]
Dylan16807 7y ago
Knowing nothing can reduce performance from peak can be more valuable than an extra 4%

pitaj 7y ago

Yeah it's weird. Why not set the single-core turbo higher?

deleted 7y ago
[deleted]
dual_basis 7y ago
Marketing.

gchamonlive 7y ago

I believe Intel processors can't boost all cores. At least some tests I have done with my notebook processor (i7 8550u - 4c8t) with `stress -c n`, being n the number of processors, show that for n > 1 the processor doesn't reach 4ghz, only about 3.7ghz, while the package temps are still at around 70 °C. Only a single core on full load reaches 4ghz before throttling.

shereadsthenews 7y ago
Yes, there's a table in the firmware that can tell you the maximum speed with N active cores. This one though has the same speed for all values of N.
clarry 7y ago
> I believe Intel processors can't boost all cores. And that's exactly what shereadsthenews's point is. They can't boost all cores, and they are not boosting any core beyond the all-core capacity if it's truly a CPU that runs at 5 GHz all the time.
- XMPPwocky 7y ago
  Turbo Boost can certainly apply to all cores- the limits you hit are TDP and time based, there, not strictly thermal. So, for example, my old laptop CPU would clock itself up to 2.7GHz on all cores... well, okay, it was a dual core, so that's not saying much, but still. But it'd only maintain that boost for a few seconds- under sustained load it dropped down to 2.5. This wasn't because of thermals, but rather because 2.7GHz was a Turbo Boost frequency, and once the PPL timer runs out...
  - XMPPwocky 7y ago
    And to explain why they don't have, say, one core boost to 5.1GHz...well, let's see what siliconlottery says. > As of 3/16/19, the top 38% of tested 9900Ks were able to hit 5.0GHz or greater. > As of 3/16/19, the top 8% of tested 9900Ks were able to hit 5.1GHz or greater. So, Intel'd cut their yield by more than a factor of four if they only let parts that could hit 5.1 into this bin. For a 2% single-core performance boost...
    - mackal 7y ago
      I think those numbers are for chips that can 5.1 GHz all core though, which is probably a lot less than 5.1 GHz single core.
      - XMPPwocky 7y ago
        As far as I know, K-series parts don't support binning of individual cores- if you have one bad core that'll only hit 5.0, 1-core turbo to 5.1 will still result in the OS scheduler periodically picking that core to use, it clocking up to 5.1, and problems resulting. Might be wrong, though.
        wtallis 7y ago
        Intel's Turbo Boost 3.0 [1] was their attempt to take advantage of the fact that some cores on a chip can clock higher than others. It does not work well in practice, because it requires too much collaboration with motherboard and OS vendors. This feature is not available on their desktop platform, which the i9-9900KS uses. [1] https://www.intel.com/content/www/us/en/architecture-and-technology/turbo-boost/turbo-boost-max-technology.html https://www.intel.com/content/www/us/en/architecture-and-tec...
rzzzt 7y ago
XTU allows setting different turbo multipliers for 1-4 active cores (but the difference from the nominal clock speed typically gets smaller as more cores become active).
mackal 7y ago
This is entirely configurable. They generally don't do all core == max boost for power consumption reasons (and I assume yield would be pretty low on chips that can do this) Desktop chips also generally don't have any AVX offset, which is almost always required for 5 GHz all core.

adamparsons 7y ago

I’d guess that the upper limit is stability rather than thermal capacity at that point

kzrdude 7y ago
What does stability mean, a bit more exactly? Just curious
- saltyshake 7y ago
  The CPU not losing its marbles when overclocked. https://devblogs.microsoft.com/oldnewthing/20050412-47/?p=35923 https://devblogs.microsoft.com/oldnewthing/20050412-47/?p=35...
- bayindirh 7y ago
  The switching speed of silicon has also some upper limit. When you drive silicon faster, it starts to make mistakes. i.e. not all electrons go the where you want them to go. This causes soft-faults and CPU re-executes the part at best, or gives you a BSOD, oops or panic at worst. This upper limit depends on process, layout, power design and power limits of the CPU. Last but, not the least, not all CPUs are created equal on a wafer. I came from an era where we hunted plain blue AMD Athlon dies for higher overclocking potential, since they were from center of the wafer and they were more stable under high load/voltage/clock. I had a 2200MHz Athon (200 x 11) which was faster then AMD's own 2200MHz Athlons, since AMD wasnt offering a 200MHz bus version of their 2200MHz parts.
  - koala_man 7y ago
    >gives you a BSOD, oops or panic at worst. That's not too bad. I'd be much more worried about code silently doing the wrong thing .
    - bayindirh 7y ago
      That's also possible. That's why overclockers run Prime95 to test their CPU stability. Also, a BSOD or panic in the wrong time can cause massive data loss. That's beyond bad sometimes. Edit: I mixed Prime95 with SuperPi. Thanks AaronFriel.

deleted 7y ago

[deleted]

Dylan16807 7y ago

Knowing nothing can reduce performance from peak can be more valuable than an extra 4%