Desktop big.little make sense in a world that separates HEDT from just desktop. That means, if you need 16 or 32 cores, you buy a HEDT chip and if you don't need 16 or 32 cores, then you buy a desktop chip. Lets assume for this discussion that the user does not really need HEDT and see what we can determine.
Assumptions:
- User does not need HEDT chip.
- User purchases typical OEM desktop.
- Typical OEM desktop is limited to 125 W of power.
- Uncore Power + iGPU Power = 20 W of power (I realize that this is a wild guess, feel free to update the math with better numbers)
- Adding 8 little cores adds another 20 W (Again a wild guess, please update with your own numbers).
- Chip performs in the same voltage/frequency curve as Comet Lake (again, another guess as I don't have Alder Lake data to work with). Chip Power with iGPU ~= 20 W + 0.163 * Number of Cores * Frequency ^ 3.182. Add the 8 little core power too as needed.
- Ignore inefficiencies as you go down the CPU line (for example, the 10600K is not the same quality chip as the 10900K).
- Little cores do half the work of big cores at the same frequency
- Software can efficiently utilize the big and little cores
Now, what if we applied that math to Alder Lake and assume money was no object. Then you'd come up with these
hypothetical possibilities:
- Hypothetical, 16 Big + 8 Little, 3.0 GHz. MT work: (16 + 8/2) * 3.0 = 59.7 Units. ST: 1 * 3.0 = 3.0 Units
- Hypothetical, 16 Big + No Little, 3.2 GHz. MT work: 16 * 3.2 = 51.1 Units. ST: 1 * 3.2 = 3.2 Units
- Hypothetical, 8 Big + 8 Little, 3.7 GHz. MT work: (8 + 8/2) * 3.7 = 44.6 Units. ST: 1 * 3.7 = 3.7 Units
- Hypothetical, 8 Big + No Little, 4.0 GHz. MT work: 8 * 4.0 = 31.8 Units. ST: 1 * 4.0 = 4.0 Units
So, looking purely at multi-threaded performance, we want as many cores as possible. But remember the very first assumption, the first assumption is that is not the workload of this user.
Yes, 16 Big + 16 little would be great, but it just doesn't meet the user's need and would cost Intel a fortune in yield. It also would seriously hurt single thread performance.
The 8+8 just is a sweet spot for a barely noticeable ~7.5% drop in single thread performance over 8+0. But it also has a sizeable ~40% multithread performance boost over 8+0. And if Intel can fully turn off the little cores so that all power is available to the big cores (unsure if that is possible so I did not include it above), then the single thread would not even be harmed.
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Lots of assumptions there. Looks like you are taking a product and positing a scenario to fit it, instead of taking what the customer needs and designing a product to fit that.
Besides, you dont have to sacrifice single core performance to get lots of cores. AMD has already shown this, since 5900x has equal or better turbo clocks than lower tier products with less cores. It will be interesting to see Alder Lake power consumption and price. I have a feeling, even with big/little for Intel, AMD will still be able to give better multicore performance with equal or less power consumption. If the rumors of improved IPC turn out for Alder Lake, I would simplify it down to 2 basic scenarios.
1. The best single core/lightly threaded performance with good multi core as well: Alder Lake. Just give me 8+0, dont bother with the small cores.
2. Best multi threaded performance: Zen 3 or 4 or whatever is available.
Of course, this could be modified by pricing. I would anticipate AL 8 + 8 would compete well with 12 zen cores. It would be much more attractive if it were priced cheaper than the 5900x. Knowing Intel though, I seriously doubt that will be the case.