5 ms·

FreeBSD Scheduling on Hybrid CPUs

119 points by fntlnz 1y ago

monster_truck 1y ago
Intel is quietly having their bulldozer moment
- johnklos 1y ago
  That's not really fair to Bulldozer CPUs. The AMD Bulldozers put a lot of new, untested ideas in to practice. Some of them paid off, while many did not, at least not in the short term. There were, however, many good ideas, and many of those lived on and helped make Ryzen what it is. Over time, Bulldozer performance has matched and exceeded contemporary Intel performance, both because compiler optimizations have made better use of the CPU and because of the slowdowns from Spectre / Meltdown affecting Intel much more than AMD. I still run an FX-8150 server and have compared it with an Intel 2600K system in many tasks. Do we think that Intel is going to use their current shitshow to make a golden age of Intel CPUs, like how Bulldozer led to Ryzen? I personally don't think so. They've put all their cheap tricks in to their CPUs, tricks which require huge slowdowns when flaws are found, and unless / until they start caring about actually doing things correctly rather than playing fast and loose with hundreds of watts, they'll keep trying to game the benchmarks, will keep having flaws and problems, and will keep losing market share.
themafia 1y ago
> Apart from some models of Alder Lake, it is now impossible to buy an Intel chip that does not have at least P (Performance) and E (Efficiency) cores. Really? I just bought one: https://www.intel.com/content/www/us/en/products/sku/236786/intel-core-i3-processor-14100f-12m-cache-up-to-4-70-ghz/specifications.html https://www.intel.com/content/www/us/en/products/sku/236786/...
- pixl97 1y ago
  How about change that to "Anything with more than 6 cores". Anything with 4 cores only has one speed of core. At 6 cores it more of a mixed bag, some have all the same cores, some have a split of performance and efficient cores. Anything over an i5 will have E cores.
  - swills 1y ago
    Hmm, I think Granite Rapids is all P-Cores and goes up to 86 cores (172 threads): https://en.wikipedia.org/wiki/Granite_Rapids https://en.wikipedia.org/wiki/Granite_Rapids
    - c0balt 1y ago
      Yep, there are still server CPUs with only P-cores. They are a bit expensive but I wouldn't expect them to drop these skews in the long term for HPC & compute bound workloads. My guess is that diamond rapids will also have some P-skews and maybe AP skews.
    - mlyle 1y ago
      Here there's weirdness, still, though because there's such a frequency difference you'll get between "low priority" and "high priority" cores.
- dehrmann 1y ago
  There are also Xeons, but it limits an OS to use in data centers.
  - dijit 1y ago
    There are workstation Xeons. Though it seems that mobile Xeons are defunct now.
- wtallis 1y ago
  > Apart from some models of Alder Lake That bit actually still applies. Intel may have branded the 14100F as Raptor Lake, but it is almost certainly Alder Lake silicon, just a higher speed bin of the 12100F. See https://www.intel.com/content/www/us/en/products/compare.html?productIds=236786,230576,132223 https://www.intel.com/content/www/us/en/products/compare.htm... and note how none of them get the higher DRAM frequency support or larger L2 caches characteristic of Raptor Lake silicon.
- ethan_smith 1y ago
  The i3-14100F is just one example - Intel still sells numerous non-hybrid models across their lineup including most i3s, Pentiums, Celerons, and many server/workstation Xeons. The documentation's claim about availability is overstated.
dehrmann 1y ago
The high-level pitch of P cores and E cores seems so elegant, but when it actually comes to scheduling, it gets messy fast. Even in a laptop running off a battery, you can't simply switch to E cores because some short-lived work might be latency-sensitive. You also can't assume long-running work should be on an E core because maybe you're anxious to get that video encoded. Even for lots of small work, different core can have different performance characteristics, and a P core might be more efficient for certain workloads.
- jcelerier 1y ago
  As a user with a laptop, the last thing I want is the OS to decide for me. I want to tell it myself "this is sensitive, put all your energy into it because I'm five minutes away from pushing that important work and I have seven minutes of battery left" or "this won't work at all if run at less than 2 GHz" vs "I must drag what I'm doing along for as long as I can, save every bit of battery possible. The computer can't know about these cases.
  - twoodfin 1y ago
    FWIW, Apple leaves it up to the app developer to specify a quality-of-service for a particular execution context: https://developer.apple.com/library/archive/documentation/Performance/Conceptual/EnergyGuide-iOS/PrioritizeWorkWithQoS.html https://developer.apple.com/library/archive/documentation/Pe...
  - 01HNNWZ0MV43FF 1y ago
    I feel like cases 1, 2, and 3 broadly fit into "Battery Saver", "Performance", and "Battery Saver" modes?
    - jcelerier 1y ago
      Yes exactly - which I set myself depending on my current use case at hand. I definitely don't want the OS to try and guess
  - bluGill 1y ago
irusensei 1y ago
Thats one of the reasons I switched back to Linux. I've bought Alder Lake and a couple of RockPro64s that have heterogenous CPU sets.
Dead_Lemon 1y ago
Maybe its just me, but this P&E arch is underwhelming and screams similar issues AMD bulldozer again. Claims of massive core counts with mediocre performance, and little control over how things are assigned to the cores. Maybe that will improve over time with improved schedulers, but I doubt it. Its looks like an architectural issue. The experience feels so inconstant, even ending up worse than the prior generations with all normal P cores with lower core counts. I'm avoiding Intel P&E CPUs with anything that needs consistent performance, as my limited experience with the new Intel chips leaves me with a bitter taste in my mouth, and a frustrating computing experience.
- DevelopingElk 1y ago
  I see the heterogeneous architectures as mostly a plus. If you want the most throughput for a highly parallel workload given a power and silicon budget 100% E cores would be best. If you have some workloads that don't parallelize well then a few P cores are best. Heterogeneous gives possibilities to optimize for both cases. There is another knob to turn, and mistakes can be made, but this should be an overall positive. My bigger concern with the newer Intel CPUs are the crashes and reliability issues that were reported.
- ksec 1y ago
  You do realise every single Smartphone has had P&E core for the past 6 - 7 years? The problem is more with Intel.

119 points by fntlnz 1y ago

monster_truck 1y ago

Intel is quietly having their bulldozer moment

johnklos 1y ago
That's not really fair to Bulldozer CPUs. The AMD Bulldozers put a lot of new, untested ideas in to practice. Some of them paid off, while many did not, at least not in the short term. There were, however, many good ideas, and many of those lived on and helped make Ryzen what it is. Over time, Bulldozer performance has matched and exceeded contemporary Intel performance, both because compiler optimizations have made better use of the CPU and because of the slowdowns from Spectre / Meltdown affecting Intel much more than AMD. I still run an FX-8150 server and have compared it with an Intel 2600K system in many tasks. Do we think that Intel is going to use their current shitshow to make a golden age of Intel CPUs, like how Bulldozer led to Ryzen? I personally don't think so. They've put all their cheap tricks in to their CPUs, tricks which require huge slowdowns when flaws are found, and unless / until they start caring about actually doing things correctly rather than playing fast and loose with hundreds of watts, they'll keep trying to game the benchmarks, will keep having flaws and problems, and will keep losing market share.

themafia 1y ago

> Apart from some models of Alder Lake, it is now impossible to buy an Intel chip that does not have at least P (Performance) and E (Efficiency) cores. Really? I just bought one: https://www.intel.com/content/www/us/en/products/sku/236786/intel-core-i3-processor-14100f-12m-cache-up-to-4-70-ghz/specifications.html https://www.intel.com/content/www/us/en/products/sku/236786/...

pixl97 1y ago
How about change that to "Anything with more than 6 cores". Anything with 4 cores only has one speed of core. At 6 cores it more of a mixed bag, some have all the same cores, some have a split of performance and efficient cores. Anything over an i5 will have E cores.
- swills 1y ago
  Hmm, I think Granite Rapids is all P-Cores and goes up to 86 cores (172 threads): https://en.wikipedia.org/wiki/Granite_Rapids https://en.wikipedia.org/wiki/Granite_Rapids
  - c0balt 1y ago
    Yep, there are still server CPUs with only P-cores. They are a bit expensive but I wouldn't expect them to drop these skews in the long term for HPC & compute bound workloads. My guess is that diamond rapids will also have some P-skews and maybe AP skews.
  - mlyle 1y ago
    Here there's weirdness, still, though because there's such a frequency difference you'll get between "low priority" and "high priority" cores.
dehrmann 1y ago
There are also Xeons, but it limits an OS to use in data centers.
- dijit 1y ago
  There are workstation Xeons. Though it seems that mobile Xeons are defunct now.
wtallis 1y ago
> Apart from some models of Alder Lake That bit actually still applies. Intel may have branded the 14100F as Raptor Lake, but it is almost certainly Alder Lake silicon, just a higher speed bin of the 12100F. See https://www.intel.com/content/www/us/en/products/compare.html?productIds=236786,230576,132223 https://www.intel.com/content/www/us/en/products/compare.htm... and note how none of them get the higher DRAM frequency support or larger L2 caches characteristic of Raptor Lake silicon.
ethan_smith 1y ago
The i3-14100F is just one example - Intel still sells numerous non-hybrid models across their lineup including most i3s, Pentiums, Celerons, and many server/workstation Xeons. The documentation's claim about availability is overstated.

dehrmann 1y ago

The high-level pitch of P cores and E cores seems so elegant, but when it actually comes to scheduling, it gets messy fast. Even in a laptop running off a battery, you can't simply switch to E cores because some short-lived work might be latency-sensitive. You also can't assume long-running work should be on an E core because maybe you're anxious to get that video encoded. Even for lots of small work, different core can have different performance characteristics, and a P core might be more efficient for certain workloads.

jcelerier 1y ago
As a user with a laptop, the last thing I want is the OS to decide for me. I want to tell it myself "this is sensitive, put all your energy into it because I'm five minutes away from pushing that important work and I have seven minutes of battery left" or "this won't work at all if run at less than 2 GHz" vs "I must drag what I'm doing along for as long as I can, save every bit of battery possible. The computer can't know about these cases.
- twoodfin 1y ago
  FWIW, Apple leaves it up to the app developer to specify a quality-of-service for a particular execution context: https://developer.apple.com/library/archive/documentation/Performance/Conceptual/EnergyGuide-iOS/PrioritizeWorkWithQoS.html https://developer.apple.com/library/archive/documentation/Pe...
- 01HNNWZ0MV43FF 1y ago
  I feel like cases 1, 2, and 3 broadly fit into "Battery Saver", "Performance", and "Battery Saver" modes?
  - jcelerier 1y ago
    Yes exactly - which I set myself depending on my current use case at hand. I definitely don't want the OS to try and guess
- bluGill 1y ago

irusensei 1y ago

Thats one of the reasons I switched back to Linux. I've bought Alder Lake and a couple of RockPro64s that have heterogenous CPU sets.

Dead_Lemon 1y ago

Maybe its just me, but this P&E arch is underwhelming and screams similar issues AMD bulldozer again. Claims of massive core counts with mediocre performance, and little control over how things are assigned to the cores. Maybe that will improve over time with improved schedulers, but I doubt it. Its looks like an architectural issue. The experience feels so inconstant, even ending up worse than the prior generations with all normal P cores with lower core counts. I'm avoiding Intel P&E CPUs with anything that needs consistent performance, as my limited experience with the new Intel chips leaves me with a bitter taste in my mouth, and a frustrating computing experience.

DevelopingElk 1y ago
I see the heterogeneous architectures as mostly a plus. If you want the most throughput for a highly parallel workload given a power and silicon budget 100% E cores would be best. If you have some workloads that don't parallelize well then a few P cores are best. Heterogeneous gives possibilities to optimize for both cases. There is another knob to turn, and mistakes can be made, but this should be an overall positive. My bigger concern with the newer Intel CPUs are the crashes and reliability issues that were reported.
ksec 1y ago
You do realise every single Smartphone has had P&E core for the past 6 - 7 years? The problem is more with Intel.