More general questions on battery life and processor efficiency

Which option is more effective in achieving battery life gains-- setting your CPU speed to adaptive, or to the lowest setting?

The lowest setting is of course, much lower than the full speed and definitely consumes less power, however, does it actually save power if you set the speed to adaptive so that the CPU can quickly throttle up if need be and complete a task faster than it would in "Lowest" mode?

Example: What would use less power? A task that takes 1 full minute to complete with 100% speed on Lowest, or the same task that takes 25 seconds with the adaptive CPU throttling up to 100% only for a fraction of the time?

I've switched my power manager settings lately to Lowest and have been getting great battery life, but I'm curious to know which mode is more efficient?

 

Adaptive.

I've been using mine in Adaptive, after changing it from Lowest, for the past 7-8 months.
Just yesterday, after 7.5 hours of "very light" use, I had 3+ hours on power manager.

your argument in your 2nd paragraph is also mine

the task with cpu spiked will consume less power since there is a baseline power draw regardless and you're adding on top of that while sitting and waiting. so the "down time" is less, and hence the min. power draw per sec added up over this time is less with adaptive.

But the real question is: how fast does the OS throttle it down in adaptive..
fast enough is the answer

 

My T500 is set to adaptive on AC power and lowest on battery. When on battery, all I generally do is type Word documents, work with spreadsheets and presentations, and browse the web, so I find that capping it at lowest prevents the CPU from ever spiking to maximum power usage.

I can get up to around 8 hours on my T500 in indoors light usage.

 

I'm inclined to say adaptive but with a few reservations.

An adaptive CPU is much more efficient if your overall system power consumption is fairly high. For example, if you are also working with a bright display, spinning HDD, and possibly utilizing the GPU the ability to complete tasks in less time will save a lot of energy.

However, if you have your display turned off (generally the least efficient part in a notebook), are running on integrated graphics, and the HDD is idle (or you use a very efficient SSD) then the "slowest" speed is no worse and may even prove more efficient for the entire task (wattage tends to increase at a higher rate than performance [especially at the higher levels]).

One other possible advantage of locking the CPU to slow is if you're machine is executing runaway processes. I found this to be worst when browsing with Firefox on sites with Flash ads. Often the flash ads would hit an infinite loop and peg the CPU to 100% (or 1/n if using a multi-core machine) while accomplishing nothing. Setting the CPU to low minimizes the efficiency penalty you pay for this kind of lazy programming (alternatively noScript & Flashblock will generally prevent this from happening).


So in short it depends, but I would generally recommend adaptive if you are running a fair amount of tasks that require a mid length (10-120 seconds) burst of CPU power.

 

Awesome replies, thanks a lot for the help. I usually don't do much on battery power, maybe just word and browsing or sometimes not even that. Occasionally it's just on with torrents running. For such low use I guess the 800Mhz option would probably fair better. I'll try them both out for a week or so and see how it goes.

Thanks again!

 

mucho drain