Re:Mispredicted branches can multiply your running times
by morelisp on Wednesday October 16, 2019 @01:23PM
(#21272901)
> speed would go down, not up (but power consumption would improve).
Power consumption per second might go down, but overall may go up, depending on how many more seconds the computation takes.
Re:Mispredicted branches can multiply your running times
by lippel82 on Wednesday October 16, 2019 @02:12PM
(#21273499)
To be slightly pedantic here: Power is energy per second, so power consumption itself would go down. Total energy consumption, which is power*time could go up.
Re:Mispredicted branches can multiply your running times
by morelisp on Wednesday October 16, 2019 @02:30PM
(#21273735)
The correction is welcome - I am just a little sad we trained a cohort of developers to care about power, but not well enough to understand that race-to-sleep is usually the best way to achieve that.
Re:Mispredicted branches can multiply your running times
by marcosdumay on Friday October 18, 2019 @08:20AM
(#21290712)
Hum... Race to sleep is usually not the best way to save power. Undervoltage is. Race to sleep just gets the spotlight once you have an extremely optimized CPU that can not be undervolted anymore in a practical way.
The rule of thumb you learned is useful for optimizing PC software, but has no place in CPU architecture discussions.
Also, "usually" leaves a lot of important cases out.
Considering the complex predictors on current PCs, we would save quite a lot of circuitry. But that circuitry is there because it is the most effective place to increase the CPU speed, if you used it for something else, speed would go down, not up (but power consumption would improve).
Also, actual clock speed isn't really relevant and has a complex relation to CPU speed. That circuitry isn't affecting clock speed, so it wouldn't change.