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.
nine_k 9 hours ago [-]
Funny enough, Unix already has user-settable priorities, aka "nice level". ACPI gives us an idea how plentiful the power is.
So, when powered by AC power, schedule everything on P cores when possible, schedule processes that eat a lot of CPU on P cores, same for any process with a negative nice value.
When powered by a battery, schedule anything with non-negative nice value on E cores, keep one P core up for real-time tasks, and for nice-below-zero tasks.
These are two extremes, but I suppose that the idea is understandable.
wtallis 9 hours ago [-]
> So, when powered by AC power, schedule everything on P cores when possible, schedule processes that eat a lot of CPU on P cores, same for any process with a negative nice value.
Even when plugged in, you may have thermal limitations. P cores will chew through your power budget more aggressively than E cores. For latency-sensitive workloads you do want to emphasize the P cores, but when throughput is the goal you'll usually be better off not ignoring the E cores, and not trying to run the P cores at high frequency where they're much less efficient. Intel started adding E cores to consumer chips in large part so they could score better on throughput-oriented multithreaded benchmarks like Cinebench; they're decent at compiling code, too, but you'll still want the P core for the linker.
Melatonic 8 hours ago [-]
Always personally disable turbo boost. Especially on laptops
casenmgreen 2 hours ago [-]
If I run a game, I limit CPU to about 50% clock speed.
Only way to stop laptop getting crazy hot and fans meaningfully reducing pressure on desk of laptop...
casenmgreen 2 hours ago [-]
I may be completely wrong, but I read that E cores are not power efficient, rather they are die space efficient.
arp242 3 hours ago [-]
That's not really how nice levels have worked traditionally, and would disallow specifying "run on Performance cores, but yield to other processes quickly".
mrheosuper 9 hours ago [-]
>when powered by AC power, schedule everything on P cores when possible
Sometime I feel like that is undesirable. It may make system consume more power, thus more heat output and louder.
nine_k 8 hours ago [-]
A laptop and a desktop certainly would balance P and E differently!
5 hours ago [-]
jcelerier 10 hours 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 9 hours ago [-]
FWIW, Apple leaves it up to the app developer to specify a quality-of-service for a particular execution context:
I feel like cases 1, 2, and 3 broadly fit into "Battery Saver", "Performance", and "Battery Saver" modes?
Dead_Lemon 60 minutes 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.
irusensei 4 hours 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.
themafia 11 hours 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.
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.
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 10 hours ago [-]
Hmm, I think Granite Rapids is all P-Cores and goes up to 86 cores (172 threads):
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 8 hours ago [-]
Here there's weirdness, still, though because there's such a frequency difference you'll get between "low priority" and "high priority" cores.
ethan_smith 6 hours 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 10 hours ago [-]
There are also Xeons, but it limits an OS to use in data centers.
dijit 5 hours ago [-]
There are workstation Xeons. Though it seems that mobile Xeons are defunct now.
So, when powered by AC power, schedule everything on P cores when possible, schedule processes that eat a lot of CPU on P cores, same for any process with a negative nice value.
When powered by a battery, schedule anything with non-negative nice value on E cores, keep one P core up for real-time tasks, and for nice-below-zero tasks.
These are two extremes, but I suppose that the idea is understandable.
Even when plugged in, you may have thermal limitations. P cores will chew through your power budget more aggressively than E cores. For latency-sensitive workloads you do want to emphasize the P cores, but when throughput is the goal you'll usually be better off not ignoring the E cores, and not trying to run the P cores at high frequency where they're much less efficient. Intel started adding E cores to consumer chips in large part so they could score better on throughput-oriented multithreaded benchmarks like Cinebench; they're decent at compiling code, too, but you'll still want the P core for the linker.
Only way to stop laptop getting crazy hot and fans meaningfully reducing pressure on desk of laptop...
Sometime I feel like that is undesirable. It may make system consume more power, thus more heat output and louder.
https://developer.apple.com/library/archive/documentation/Pe...
Really? I just bought one:
https://www.intel.com/content/www/us/en/products/sku/236786/...
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.htm... and note how none of them get the higher DRAM frequency support or larger L2 caches characteristic of Raptor Lake silicon.
https://en.wikipedia.org/wiki/Granite_Rapids
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.