4 ms·

That claim would be highly suspect in general, given that a desktop CPU has at least 10 times more headroom in power consumption. For such a claim to be true,

by 21 8y ago

That claim would be highly suspect in general, given that a desktop CPU has at least 10 times more headroom in power consumption. For such a claim to be true, you would have to expect that the phone CPU is somehow 10 times more efficient per Watt, while having the same kind of architecture (general CPU, not GPU/TPU/...).

deleted 8y ago
[deleted]
MBCook 8y ago
It’s perfectly possible that the iPhone CPU can’t run 4 hours straight due to heat issues in its enclosure while a desktop CPU can. But that could be fixed. Intel has not been optimizing for TDP/power draw as aggressively as Apple has. Apple started from that position and went up in performance. Intel started more in performance and had tried to keep TDP in check.
Symmetry 8y ago
If you give the i5 it's full voltage and crank up the clock speed it'll totally beat an Apple chip. But in order to fit in a Macbook Air's power envelope you need to really throttle things back and a chip that's designed to operate in that regime has a big advantage over a chip that isn't.
Const-me 8y ago
I think he might be correct. Apple A11 has 297 GFlops CPU performance. (1) That “7th gen i5” is apparently i5-7360U. 32 FLOPs/cycle/core (2) * 2 cores * 3.50 GHz (=max turbo) = 224 GFlops. > the phone CPU is somehow 10 times more efficient per Watt Not 10 times. The i5’s TDP is just 15W. I don’t know about A11 but high-end Qualcomm chips can be up to 5-6W, just 3 times difference. > while having the same kind of architecture (general CPU, not GPU/TPU). That’s a continuum. They both CPUs, they both have SIMD that’s how they achieve that high flop/cycle, but the architecture can be quite different. A11 has 6 cores. Intel spends many transistors, and therefore energy, doing very complicated things: branch prediction, indirect branch prediction, cache synchronization between cores, speculative execution… Apple has full control over OS and software, they can probably get away with not doing some of these. Intel and AMD have to maintain compatibility with all software (including single threaded), built by all compilers and languages, that’s why they have fewer tradeoffs available to them. (1) https://forum.beyond3d.com/posts/2021926/ https://forum.beyond3d.com/posts/2021926/ (2) https://stackoverflow.com/a/15657772/126995 https://stackoverflow.com/a/15657772/126995
imtringued 8y ago
It is true but at the same time it is not. Geekbench measures the unthrottled performance of a CPU. One thing you have to consider is that ARM SoCs contain a cluster of heterogenous cores. A high performance low efficiency core for bursty workloads or games and a highly efficient core for "sleepless" standby. What happens is that people see a benchmark and they see low power consumption and now conclude that it must have 10 times better performance per watt. x86 is bad, ARM is good But the thing is you cannot have your cake and eat it too. The ARM SoC is clearly more efficient but only during standby or low intensity workloads and because everything is integrated into a single chip. As soon as you use a constant CPU/GPU intensive workload like servers or video games or even just google maps [1] you will have the same energy efficiency as intel chips. [1] My phone battery barely lasts 2 hours with google maps

by 21 8y ago

deleted 8y ago

[deleted]

MBCook 8y ago

It’s perfectly possible that the iPhone CPU can’t run 4 hours straight due to heat issues in its enclosure while a desktop CPU can. But that could be fixed. Intel has not been optimizing for TDP/power draw as aggressively as Apple has. Apple started from that position and went up in performance. Intel started more in performance and had tried to keep TDP in check.

Symmetry 8y ago

If you give the i5 it's full voltage and crank up the clock speed it'll totally beat an Apple chip. But in order to fit in a Macbook Air's power envelope you need to really throttle things back and a chip that's designed to operate in that regime has a big advantage over a chip that isn't.

Const-me 8y ago

I think he might be correct. Apple A11 has 297 GFlops CPU performance. (1) That “7th gen i5” is apparently i5-7360U. 32 FLOPs/cycle/core (2) * 2 cores * 3.50 GHz (=max turbo) = 224 GFlops. > the phone CPU is somehow 10 times more efficient per Watt Not 10 times. The i5’s TDP is just 15W. I don’t know about A11 but high-end Qualcomm chips can be up to 5-6W, just 3 times difference. > while having the same kind of architecture (general CPU, not GPU/TPU). That’s a continuum. They both CPUs, they both have SIMD that’s how they achieve that high flop/cycle, but the architecture can be quite different. A11 has 6 cores. Intel spends many transistors, and therefore energy, doing very complicated things: branch prediction, indirect branch prediction, cache synchronization between cores, speculative execution… Apple has full control over OS and software, they can probably get away with not doing some of these. Intel and AMD have to maintain compatibility with all software (including single threaded), built by all compilers and languages, that’s why they have fewer tradeoffs available to them. (1) https://forum.beyond3d.com/posts/2021926/ https://forum.beyond3d.com/posts/2021926/ (2) https://stackoverflow.com/a/15657772/126995 https://stackoverflow.com/a/15657772/126995

imtringued 8y ago

It is true but at the same time it is not. Geekbench measures the unthrottled performance of a CPU. One thing you have to consider is that ARM SoCs contain a cluster of heterogenous cores. A high performance low efficiency core for bursty workloads or games and a highly efficient core for "sleepless" standby. What happens is that people see a benchmark and they see low power consumption and now conclude that it must have 10 times better performance per watt. x86 is bad, ARM is good But the thing is you cannot have your cake and eat it too. The ARM SoC is clearly more efficient but only during standby or low intensity workloads and because everything is integrated into a single chip. As soon as you use a constant CPU/GPU intensive workload like servers or video games or even just google maps [1] you will have the same energy efficiency as intel chips. [1] My phone battery barely lasts 2 hours with google maps