4 ms·

> It isn’t far fetched that a device would reduce power consumption when on battery, it makes the device last longer, makes users happier. Does it? If I reduce

> It isn’t far fetched that a device would reduce power consumption when on battery, it makes the device last longer, makes users happier. Does it? If I reduce the amount of power available to complete a task, but proceed to complete the task anyways, doesn't the phone now need to potentially have the peripherals (particularly, the screen) on for longer as the user waits for a task that has been slowed down to complete, consuming more energy than had it completed the task using 100% CPU? (Unless using 80% of the CPU can accomplish the same task using less energy (not power) and recoup enough to make up for the losses incurred by needing extra time.) It isn't intuitive to me at all that what we're doing isn't making phones useless so that their battery lasts all day.

jerf 9y ago
"It depends": https://pdfs.semanticscholar.org/6611/bc084fbaf1845b1bf54cc72d1c143d25083d.pdf https://pdfs.semanticscholar.org/6611/bc084fbaf1845b1bf54cc7... From the abstract: "We evaluate three systems - a clock throttled Pentium laptop, a frequency scaled PowerPC platform, and a voltage scaled system.... on the Pentium-based system, it is energy efficient to run only at the highest frequency, while on the PowerPC-based system, it is energy efficient to run at the lowest frequency point." So it can go either way, depending on a lot of the local factors.
daxfohl 9y ago
I'm not an expert, but I think the high-power modes do things like very aggressive caching and branch prediction, etc. to speed things up. So there's a bunch of energy spent on e.g. transferring and storing memory that may never be used, or computing branches that may never be hit. Lower power modes don't do this as aggressively, so they only consume energy for results that will be used. Plus I'm pretty sure your base voltage has to be higher to run at higher frequency, and non linearly so, to counter various electrostatic effects.
deleted 9y ago
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ggg9990 9y ago
Not really. Most people are not computing primes on their phones, they are surfing Facebook and Instagram. Since it’s a pointless activity there isn’t the concept of “completing a task” — they will just think “I Facebooked for three hours instead of 2” instead of “I got to see 500 photos in 2 hours rather than 400 photos in 3 hours.”

jerf 9y ago

"It depends": https://pdfs.semanticscholar.org/6611/bc084fbaf1845b1bf54cc72d1c143d25083d.pdf https://pdfs.semanticscholar.org/6611/bc084fbaf1845b1bf54cc7... From the abstract: "We evaluate three systems - a clock throttled Pentium laptop, a frequency scaled PowerPC platform, and a voltage scaled system.... on the Pentium-based system, it is energy efficient to run only at the highest frequency, while on the PowerPC-based system, it is energy efficient to run at the lowest frequency point." So it can go either way, depending on a lot of the local factors.

daxfohl 9y ago

I'm not an expert, but I think the high-power modes do things like very aggressive caching and branch prediction, etc. to speed things up. So there's a bunch of energy spent on e.g. transferring and storing memory that may never be used, or computing branches that may never be hit. Lower power modes don't do this as aggressively, so they only consume energy for results that will be used. Plus I'm pretty sure your base voltage has to be higher to run at higher frequency, and non linearly so, to counter various electrostatic effects.

deleted 9y ago

[deleted]

ggg9990 9y ago

Not really. Most people are not computing primes on their phones, they are surfing Facebook and Instagram. Since it’s a pointless activity there isn’t the concept of “completing a task” — they will just think “I Facebooked for three hours instead of 2” instead of “I got to see 500 photos in 2 hours rather than 400 photos in 3 hours.”