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Skymont: Intel's E-Cores reach for the Sky (2024)

(chipsandcheese.com)
128 points ksec | 2 comments | 18 Jan 25 19:27 UTC | HN request time: 0.525s | source
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rwmj ◴[18 Jan 25 22:54 UTC] No.42752085[source]▶
Slightly off topic, but if I'm aiming to get the fastest 'make -jN' for some random C project (such as the kernel) should I set N = #P [threads] + #E, or just the #P, or something else? Basically, is there a case where using the E cores slows a compile down? Or is power management a factor?

I timed it on the single Intel machine I have access to with E-cores and setting N = #P + #E was in fact the fastest, but I wonder if that's a general rule.

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1. wmf ◴[18 Jan 25 23:05 UTC] No.42752141[source]▶
Power management is a factor because the cores "steal" power from each other. However the E-cores are more efficient so slowing down P-cores and giving some of their power to the E-cores increases the efficiency and performance of the chip overall. In general you're better off using all the cores.
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2. jeffbee ◴[19 Jan 25 00:49 UTC] No.42752686[source]▶
I suggest this depends on the exact model you are using. On Alder/Raptor Lake, the E-cores run at 4.5GHz which is completely futile, and in doing so they heat their adjacent P-cores, because 2x E-core clusters can easily draw 135W or more. This can significantly cut into the headroom of the nearby P. Arrow Lake-S has rearranged the E-cores.