CPU underclocking and battery life

[-sandro-]

Hello,
Are there any benchmarks that show using Power Saver plans in Windows that actually underclocks the CPU make the battery last longer?
I had this doubt cause using this plan I notice the system running slower and things take longer to complete...even loading a web page.

So if it's the CPU uses a little bit less of power to complete a task in double the time wouldn't this make things worse or equal to the standard settings?

Thanks!

 

[LTC8K6]

Hello,
Are there any benchmarks that show using Power Saver plans in Windows that actually underclocks the CPU make the battery last longer?
I had this doubt cause using this plan I notice the system running slower and things take longer to complete...even loading a web page.

So if it's the CPU uses a little bit less of power to complete a task in double the time wouldn't this make things worse or equal to the standard settings?

Thanks!

The CPU typically clocks back up to complete the task, so it should not be taking longer.

Benchmarks run at High Performance, Balanced, and Power Saver should not show a huge difference with a modern CPU.

I would find it odd to find web pages loading slower simply because I had the OS set to Balanced.

 

[-sandro-]

The CPU typically clocks back up to complete the task, so it should not be taking longer.

Benchmarks run at High Performance, Balanced, and Power Saver should not show a huge difference with a modern CPU.

I would find it odd to find web pages loading slower simply because I had the OS set to Balanced.

I'm not talking about Balanced which is the standard CPU behavior. I definitely put it wrong . I meant Power Saver plans that lock the clock to the minimum and don't allow turbo mode and stuff like that.

 

[LTC8K6]

Is this like that argument about fuel economy?

If I drive at 55mph for a 500 mile trip, and the trip takes 9 hours, versus driving at 75mph and having the trip take 6.5 hours. Did I really save fuel driving 55mph?

I have actually heard this argument about downclocking the CPU to save energy, and whether it actually saves energy overall.

I can't recall a resolution.

 

[Ketchup]

You can actually set the maximum processor state in Windows power options (in percentages). But the computer spends most of its time at the lowest level for normal activity, so I don't know that this would come out as much of a benefit.

I know that on many laptops, turning the screen brightness down is one of the best ways to save battery life. What kind of hardware are we talking about, and how old is it?

 

[Mr Evil]

Is this like that argument about fuel economy?

If I drive at 55mph for a 500 mile trip, and the trip takes 9 hours, versus driving at 75mph and having the trip take 6.5 hours. Did I really save fuel driving 55mph?

I have actually heard this argument about downclocking the CPU to save energy, and whether it actually saves energy overall.

I can't recall a resolution.

There are two parts to the power consumption of a PC:
1) Fixed losses that don't depend on CPU clock speed.
2) Losses that are a function of clock speed.

As you decrease clock speed, the total energy consumed by 1) increases because tasks take longer to complete. If you increase clock speed, the total energy consumed by 2) increases (because it increases faster than the decrease in the time to complete a task). Therefore there is an optimum clock speed somewhere in the middle to minimize the energy consumed for a given task.

It's the same for cars, which are inefficient at both very high and very low speeds.

 

[LTC8K6]

There are two parts to the power consumption of a PC:
1) Fixed losses that don't depend on CPU clock speed.
2) Losses that are a function of clock speed.

As you decrease clock speed, the total energy consumed by 1) increases because tasks take longer to complete. If you increase clock speed, the total energy consumed by 2) increases (because it increases faster than the decrease in the time to complete a task). Therefore there is an optimum clock speed somewhere in the middle to minimize the energy consumed for a given task.

It's the same for cars, which are inefficient at both very high and very low speeds.

For cars, the answer is simple math.

500 miles at 25mpg = 20 gallons used.
500 miles at 30mpg = 16.7 gallons used.

55mph will use less fuel, even though it takes longer.

For CPUs, it's not so simple.

Generally, I just leave Windows in balanced mode on the laptop and don't think that much about battery life.

I generally only think about battery life when I lose power at the house.

 

[Mr Evil]

For cars, the answer is simple math.

500 miles at 25mpg = 20 gallons used.
500 miles at 30mpg = 16.7 gallons used.

55mph will use less fuel, even though it takes longer...

Now calculate how much fuel will be used at <55mph.

...For CPUs, it's not so simple...

It's pretty much the same. If you were to plot the total energy consumed for a particular task against CPU frequency, it would look something like this

|        |
 \      /
  \    /
   \__/

with a minimum in the middle. Determining what frequency that occurs at is left as an exercise for the reader.

 

[LTC8K6]

I was answering my own post/question, not a general question about fuel economy.

Also CPU's do not have all of the external influences on efficiency that a car engine has.

I suppose you could equate a background task with a headwind or a hill.