A Hybrid/Heterogeneous Design

Developing a processor with two different types of core is not a new concept – there are billions of smartphones that have exactly that inside them, running Android or iOS, as well as IoT and embedded systems. We’ve also seen it on Windows, cropping up on Qualcomm’s Windows on Snapdragon mobile notebooks, as well as Intel’s previous Lakefield design. Lakefield was the first x86 hybrid design in that context, and Alder Lake is the more mass-market realization of that plan.

A processor with two different types of core disrupts the typical view of how we might assume a computer works. At the basic level, it has been taught that a modern machine is consistent – every CPU has the same performance, processes the same data at the same rate, has the same latency to memory, the same latency to each other, and everything is equal. This is a straightforward homogenous design that’s very easy to write software for.

Once we start considering that not every core has the same latency to memory, moving up to a situation where there are different aspects of a chip that do different things at different speeds and efficiencies, now we move into a heterogeneous design scenario. In this instance, it becomes more complex to understand what resources are available, and how to use them in the best light. Obviously, it makes sense to make it all transparent to the user.

With Intel’s Alder Lake, we have two types of cores: high performance/P-cores, built on the Golden Cove microarchitecture, and high efficiency/E-cores, built on the Gracemont microarchitecture. Each of these cores are designed for different optimization points – P-cores have a super-wide performance window and go for peak performance, while E-cores focus on saving power at half the frequency, or lower, where the P-core might be inefficient.

This means that if there is a background task waiting on data, or something that isn’t latency-sensitive, it can work on the E-cores in the background and save power. When a user needs speed and power, the system can load up the P-cores with work so it can finish the fastest. Alternatively, if a workload is more throughput sensitive than latency-sensitive, it can be split across both P-cores and E-cores for peak throughput.

For performance, Intel lists a single P-core as ~19% better than a core in Rocket Lake 11th Gen, while a single E-core can offer better performance than a Comet Lake 10th Gen core. Efficiency is similarly aimed to be competitive, with Intel saying a Core i9-12900K with all 16C/24T running at a fixed 65 W will equal its previous generation Core i9-11900K 8C/16T flagship at 250 W. A lot of that will be that having more cores at a lower frequency is more efficient than a few cores at peak frequency (as we see in GPUs), however an effective 4x performance per watt improvement requires deeper investigation in our review.

As a result, the P-cores and E-cores look very different. A deeper explanation can be found in our Alder Lake microarchitecture deep dive, but the E-cores end up being much smaller, such that four of them are roughly in the same area as a single P-core. This creates an interesting dynamic, as Intel highlighted back at its Architecture Day: A single P-core provides the best latency-sensitive performance, but a group of E-cores would beat a P-core in performance per watt, arguably at the same performance level.

However, one big question in all of this is how these workloads end up on the right cores in the first place? Enter Thread Director (more on the next page).

A Word on L1, L2, and L3 Cache

Users with an astute eye will notice that Intel’s diagrams relating to core counts and cache amounts are representations, and some of the numbers on a deeper inspection need some explanation.

For the cores, the processor design is physically split into 10 segments.

A segment contains either a P-core or a set of four E-cores, due to their relative size and functionality. Each P-core has 1.25 MiB of private L2 cache, which a group of four E-cores has 2 MiB of shared L2 cache.

This is backed by a large shared L3 cache, totaling 30 MiB. Intel’s diagram shows that there are 10 LLC segments which should mean 3.0 MiB each, right? However, moving from Core i9 to Core i7, we only lose one segment (one group of four E-cores), so how come 5.0 MiB is lost from the total L3? Looking at the processor tables makes less sense.


Please note that the following is conjecture; we're awaiting confirmation from Intel that this is indeed the case.

It’s because there are more than 10 LLC slices – there’s actually 12 of them, and they’re each 2.5 MiB.  It’s likely that either each group of E-cores has two slices each, or there are extra ring stops for more cache.

Each of the P-cores has a 2.5 MiB slice of L3 cache, with eight cores making 20 MiB of the total. This leaves 10 MiB between two groups of four E-cores, suggesting that either each group has 5.0 MiB of L3 cache split into two 2.5 MiB slices, or there are two extra LLC slices on Intel’s interconnect.

Alder Lake Cache
AnandTech Cores
IGP Base
i9-12900K 8+8/24 8x1.25
30 770 125 241 $589
i9-12900KF 8+8/24 8x1.25
30 - 125 241 $564
i7-12700K 8+4/20 8x1.25
25 770 125 190 $409
i7-12700KF 8+4/20 8x1.25
25 - 125 190 $384
i5-12600K 6+4/20 6x1.25
20 770 125 150 $289
i5-12600KF 6+4/20 6.125
20 - 125 150 $264

This is important because moving from Core i9 to Core i7, we lose 4xE-cores, but also lose 5.0 MiB of L3 cache, making 25 MiB as listed in the table. Then from Core i7 to Core i5, two P-cores are lost, totaling another 5.0 MiB of L3 cache, going down to 20 MiB. So while Intel’s diagram shows 10 distinct core/LLC segments, there are actually 12. I suspect that if both sets of E-cores are disabled, so we end up with a processor with eight P-cores, 20 MiB of L3 cache will be shown.

Intel Announces 12th Gen Core Alder Lake Thread Director: Windows 11 Does It Best
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  • DigitalFreak - Wednesday, October 27, 2021 - link

    Fanboi says what?
  • Kangal - Friday, October 29, 2021 - link


    But to get a little serious, I don't think Intel is going to win with their big.LITTLE architecture. I feel like ARM has a huge lead on the 15W (or less) demographic. So it would make sense for x86 designers to double-down on their performance lead in the higher thermal envelope. That's what AMD is (seemingly) going for with its focus on lower-latency Infinity Fabric, +5nm node to clock higher, and their 3D-Stacking of Cache. Not to mention all the help from DDR5, Pcie 5, nVme, Wifi 6 etc etc.

    Intel's approach will win them back the Laptop segment, but they won't be winning the tablet segment back from ARM. And even the Gaming Laptop segment won't be an outright victory against AMD's offerings, not to mention the New MacBook Pros. If anything, Intel should have capitalised on their Atom efficiency cores, and do little.BIG computing in like 2018.

    Servers is a position where Intel may see improvements. But it's still in favour of AMD for now and the near future. The bigger threat comes from next-gen ARM-servers. I doubt anything from the left-field will come, RISC-V is still a paperlaunch/niche for the next few years.

    So while I think Intel is (FINALLY) becoming competitive against AMD, I don't think they have enough to go on. Their node is still inferior. Their Xe-Graphics are still inferior to RDNA-2. And they still lag behind AMD's Cores when you factor in Infinity-Fabric and 3D-Cache. Not to mention that the system/kernel is not quiet optimised yet (let alone individual programs) when thinking about Windows11.

    For now, we have to choose from:
    Android, iOS, macOS, Windows
    RISC-V, ARM, Apple-ARM, Intel, AMD.
    ARM-Mali, PowerVR, Apple-Graphics, Nvidia, AMD RDNA.
  • Silver5urfer - Thursday, October 28, 2021 - link

    What is this fanboy junk...sigh.

    ADL demands Windows 11 POS, you want to shill for the HW which demands installing a strictly mobile junk copied OS with zero respect to computing factor on top where they are saying VBS is mandatory on all OEM machines and purposefully nuked AMD L3 performance ?

    I have a positive opinion on this ADL but it has insane changes, like Intel ITD drama who wants to endure that band aid solution of Intel with 2 layer system in between the OS and CPU. On top the major issue being socket longevity. How long this socket will retain it's value and will Intel release another Z790 next year ? No idea.

    Now for your AMD bashing, Zen 3 wiped the floor with 2 generations of processors yeah they have bugs while OCing and DRAM tuning, but if you run at stock no issues and performs very well competitively. And for the ADL performance, it's honestly a joke. Because ADL has small trash cores since Intel wants to sell more BGA junk and they cannot beat the performance with more cores due to 10nm heat.

    Raptor Joke lol so ADL CPU is going to be EOLed under a year lmao, just like 11900K ? 2 CPUs in succession. While 10900K still stands strong. That's Intel for you. Meanwhile AMD's Zen 3 is now ready for 2022 action as well with AM4 and 3D V Cache. Keep using the yearly socket refresh and chipset refresh and CPU refresh while coming here and spout nonsensical load.

    Finally pay up DDR5 tax and premium premature trash DDR5 quality, by 2023-2024 DDR5 will be matured and all ADL buyers will weep hard.

    Now for the closure. Zen 4 is going to steamroll over Raptor Joke, 100% garunteed. Do you think these companies operate without knowing what their competitor is doing ? they operate 2 years ahead of cycle internally. Plus AM4 experience is very important for AMD to fix the bugs from Platform to CPU. Ultimately they cleared out saying we are not using joker big little design. A full far Zen 4, massive price increase is also coming from them, the IPC boost and the ST SMT performance will send fanboys to darkages.
  • Silver5urfer - Thursday, October 28, 2021 - link

    I forgot to post important thing, be happy that you have AMD as competition else Intel would have been selling you 4C CPUs even in 2021 and AMD is pushing x86 to next level, if that design dies or stagnates PC will die. Keep the x86 alive if you want to own a computer not a consumable garbage ARM product.
  • MaxIT - Thursday, October 28, 2021 - link

    That works both ways: AMD dominion is not welcomed in the same way. Did you see what AMD did with prices ? AMD and Intel are the same: when they think they are above competitors, they start taxing customers. Let them fight to prevail: we customers will be the winners
  • Qasar - Thursday, October 28, 2021 - link

    " Did you see what AMD did with prices ? " you referring to the $50 price increase between zen 2 and 3 ? 50 bucks is nothing, compared to how much intel kept raising their prices over the years before zen 1 was released. but yet, very few complained about that.
  • Oxford Guy - Friday, October 29, 2021 - link

    That $50 is a response to the inflation that has been happening from all of the Covid money printing.
  • mode_13h - Friday, October 29, 2021 - link

    It's not only money-printing. There are legit shortages due to outbreaks in factories, and worker-shortages in certain sectors.

    I suspect one reason for the trucker shortage, in the US, is that truck drivers tend to be older and overweight, which are both risk factors for complications from Covid-19 (which the nature of their job also increased their exposure towards). So, I truly wonder how much the US truck driver shortage is due to drivers unable to continue performing their duties due to complications (or death).
  • Spunjji - Friday, October 29, 2021 - link

    @mode_13h - It's a good point. A lot of chatter about the effects of COVID seems to ignore how many people more than usual died. It's not world-war levels of death, but systems subject to stress have to eat into margins to cope, and a lot of the world's financial and supply-chain systems were already under stress from tariffs and sustained economic strife when COVID hit - so there weren't a lot of margins left.
  • mode_13h - Saturday, October 30, 2021 - link

    @Spunjji a lot more people have long-term effects from Covid-19 than the ones who died. Death is just the worst outcome, but there are many people unable to function at the same level as before. And I'm not only talking about "long Covid", where the immune system seems to be stuck in an overstimulated state, but other sorts of cardiovascular and organ damage it can cause.

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