3 ms·

Has anyone actually measured this on a laptop? My view is that this works for CPU heavy tasks, but not for low-frequency repeated background tasks like browser

Has anyone actually measured this on a laptop? My view is that this works for CPU heavy tasks, but not for low-frequency repeated background tasks like browser window drawing, where if you speed up your CPU you just burn energy to get a higher framerate, something you generally don't care about on powersave. So optimally you'd want to clock up for "burst tasks" and keep freq low for "per-frame tasks". But I don't know of a scheduler that does that, or even how it could do it. But if you assume most of your battery loss will be to frame tasks, powersave makes sense.

saagarjha 5y ago
These kinds of things do get used in laptops–the keyword you're looking for is "race to idle", as the processor quickly clocks up and then rushes back to a lower-frequency state or even goes back to sleep. On the mobile side, I do know that Apple did work a couple years back to scale up to maximum clock rate very quickly to handle user-interactive tasks: https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-review-unveiling-the-silicon-secrets/6 https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-re.... Then they'd ramp it back down to save on battery life.
- FeepingCreature 5y ago
  Yeah but are there actually stats that this saves power in daily use?
  - saagarjha 5y ago
    I am not a hardware engineer, so I don't have actual stats on me, unfortunately. But the reasoning behind it makes sense: https://mjg59.livejournal.com/88608.html https://mjg59.livejournal.com/88608.html. Given that everyone is doing it, I am sure that there is data that shows that; I just don't have it :P
  - hnaccount_rng 5y ago
    Well you can take the battery size (and screen times you get from those). iPhone batteries are tiny compared to android. Like seriously tiny that my 10Wh Powerbank can charge it 5 times with some to spare (I only really get 4 due to losses but still). So yes comparing iPhones to anything else highly suggests that the tuning Apple did pays off. That being said: I’m not aware of a useful comparison. I’m not even sure how you would design something like that, ie what would you like to keep constant?

saagarjha 5y ago

These kinds of things do get used in laptops–the keyword you're looking for is "race to idle", as the processor quickly clocks up and then rushes back to a lower-frequency state or even goes back to sleep. On the mobile side, I do know that Apple did work a couple years back to scale up to maximum clock rate very quickly to handle user-interactive tasks: https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-review-unveiling-the-silicon-secrets/6 https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-re.... Then they'd ramp it back down to save on battery life.

FeepingCreature 5y ago
Yeah but are there actually stats that this saves power in daily use?
- saagarjha 5y ago
  I am not a hardware engineer, so I don't have actual stats on me, unfortunately. But the reasoning behind it makes sense: https://mjg59.livejournal.com/88608.html https://mjg59.livejournal.com/88608.html. Given that everyone is doing it, I am sure that there is data that shows that; I just don't have it :P
- hnaccount_rng 5y ago
  Well you can take the battery size (and screen times you get from those). iPhone batteries are tiny compared to android. Like seriously tiny that my 10Wh Powerbank can charge it 5 times with some to spare (I only really get 4 due to losses but still). So yes comparing iPhones to anything else highly suggests that the tuning Apple did pays off. That being said: I’m not aware of a useful comparison. I’m not even sure how you would design something like that, ie what would you like to keep constant?