Comparing i3-5015U, i5-5250U and i7-5650U TDP & performance, layman's terms

[virtuality]

Key data:

i3-5015U (Toshiba Chromebook 2): http://ark.intel.com/products/84698/Intel-Core-i3-5015U-Processor-3M-Cache-2_10-GHz
TDP: 15 W
Configurable TDP-down: 10 W
Processor Base Frequency 2.1 GHz
Geekbench 3 Windows 64-bit, single-core score: 2300

i5-5250U (MacBook Air 2015): http://ark.intel.com/products/84984/Intel-Core-i5-5250U-Processor-3M-Cache-up-to-2_70-GHz
TDP: 15 W
Configurable TDP-down: 9.5 W
Processor Base Frequency: 1.6 GHz
Max Turbo Frequency: 2.7 GHz
Geekbench 3 Windows 64-bit, single-core score: 2900

i7-5650U (MacBook Air 2015): http://ark.intel.com/products/84995/Intel-Core-i7-5650U-Processor-4M-Cache-up-to-3_20-GHz
TDP: 15 W
Configurable TDP-down: 9.5 W
Processor Base Frequency: 2.2 GHz
Max Turbo Frequency: 3.1 GHz
Geekbench 3 Windows 64-bit, single-core score: 3300

Questions:
- When calculating Geekbench score, do the i5 and i7 processors run on base frequency, or turbo frequency?
- I (think I, at least on the surface) understand i5 and i7's Processor Base Frequency, Max Turbo Frequency, TDP, Configurable TDP-down; but how does the i3 has a Configurable TDP-down, if it operates on a single frequency?

Takeaway:
- TDP is just 0.5 W more for the i3 than to the i5 and i7
- The i3 seems, at least in some odd way more power efficient, if running it on 2.1 GHZ generates only a little more heat than running the i5 on 1.6 GHz (I might get this totally wrong, though). Sure, in the end the i5 ha s a higher Geekbench score, because better architecture
- The i7 is sure more efficient than the i5, same TDP, higher clock speeds, higher Geekbench scores as a result. How does it do it? But any difference in their arcitectures?

I'm not a CPU expert like probably many of you here. In layman's terms, please. Maybe I want to read a good, introductory article on all these; thanks!

 

[know of fence]

Base frequency is a bit of misnomer, because it is the frequency that is sustainable on all cores maintaining TDP, rather than lowest frequency possible. It's the "base" frequency under 100% CPU load.
A CPU is most power efficient running at lowest frequency possible. Thus the CPU actually reduces clock way down to 0.8 GHz when not it use or any other frequency in between 0.8 GHz and Base GHz when under moderate use, which some people call dynamic voltage and frequency scaling, AMD calls theirs "Cool'n'Quiet" Intel calls theirs Speedstep or EIST.
Max Turbo frequency can only be achieved when using a single core, a lower turbo when running 2 cores and so forth as long as the TDP allows it.

Now Configuarable TDP-down (configuarable TDP down Frequency : 600 MHZ) is something new and ark.intel.com doesn't explain it well, however the only way it makes sense to me is this: Both Base and Turbo are shifted by 600 MHz. For the core i3 running in the 10 W down-mode this means Base frequency is 1.5 GHz.

 

[ShintaiDK]

Base frequency is a bit of misnomer, because it is the frequency that is sustainable on all cores maintaining TDP, rather than lowest frequency possible. It's the "base" frequency under 100% CPU load.

That's not correct.

 

[sm625]

For single core mostly non-AVX benchmarks, the processor will run at or near its max turbo speed for the majority of the test. Also, a mobile i7 is not necessarily more efficient than a mobile i5. They are the same silicon and there is no real guarantee that it is even binned any higher. If you put a meter right on the power supply, you will generally see that the i7 with its higher clocks is still using more power even if it is binned higher. You can see this in the battery life tests of various i5 and i7 notebooks.

 

[know of fence]

All of your examples are dual core Broadwell, which means they have pretty much the same architecture, the i3 disables hyperthreading Turbo and also some graphics units, but they are otherwise very similar with similar power efficiency. Power efficiency varies from chip to chip a little, which is referenced as binning, and power efficiency varies a lot with frequency.
15 W also means that the thin and cramped laptop chassis doesn't allow for heat dissipation from the CPU+iGPU higher than 15 W.

For single core mostly non-AVX benchmarks, the processor will run at or near its max turbo speed for the majority of the test. Also, a mobile i7 is not necessarily more efficient than a mobile i5. They are the same silicon and there is no real guarantee that it is even binned any higher. If you put a meter right on the power supply, you will generally see that the i7 with its higher clocks is still using more power even if it is binned higher. You can see this in the battery life tests of various i5 and i7 notebooks.

QFT. The fact that Intel calls their dual cores, i5 and i7 is already misleading and suggestive of a parity to desktops that simply isn't there.
But their value comes from the fact, that they can achieve high burst performance, which makes the i7 @ 3.1 GHz almost 50% more responsive than the i3 @ 2.1 GHz, even though base frequency is similar. Geek bench mirrors that assumption; with a 2300 +43% = 3300 score.

 

[coercitiv]

the i3 disables hyperthreading and also some graphics units

The i3 has hyperthreading and GPU units are not disabled, they are different chips with different GPU configurations. (GT2 vs. GT3)

 

[Rngwn]

The i3 has hyperthreading and GPU units are not disabled, they are different chips with different GPU configurations. (GT2 vs. GT3)

Except that Intel disabled ONE EUs on the i3 50xxUs because reasons. Those parts only have 23 EUs instead of 24.

 

[coercitiv]

Except that Intel disabled ONE EUs on the i3 50xxUs because reasons. Those parts only have 23 EUs instead of 24.

Nevertheless the important difference is GT2 vs GT3, 24EU vs 48EU. Granted the i3 comes with 23EUs, so I stand corrected.

 

[know of fence]

The i3 has hyperthreading and GPU units are not disabled, they are different chips with different GPU configurations. (GT2 vs. GT3)

Sorry, I meant to say Turbo, not hyperthreading. And you are also right about GT2 (5500) and GT3 (6000) both are available with either i5 or i7 in different SKUs. What is interesting though, is that more graphics (twice as many EUs) means it encroaches on the TDP, which in turn means that the CPUs with the bigger "Intel HD Graphics 6000" are forced to have lower CPU Base clocks.
It seems that the GT2 versions of i7, i5 and i3 are cut from the same cloth/wafer? Holy shit, 281 $ for the i3 Broadwell.
I'd like to know just what kind of voltages they are running at, though that's an information that the press isn't willing and the forums aren't able to provide.

 

[Dufus]

Geekbench3 will typically report the HFM aka base frequency regardless if the CPU is running a much higher turbo frequency. Also there's an appreciable difference when running the 64-bit bench vs the 32-bit bench. TDP is a specification and not the maximum power the CPU can use. i3/5/7 is "supposed" to designate performance of low, mid and high. cTDP can change the HFM, base frequency as well as TDP sku spec.