Back in 2006, I examined the power usage of my Dell Inspiron 300M laptop. It was the first ultraportable I ever owned, and I fell in love with it. I stuck it out as long as possible on that wonderful little laptop until the true heir to the ultraportable throne was unveiled: the Dell XPS M1330. The specs are much better, as you'd expect after almost five years. But what about power consumption? How much has that changed? Let's find out.
Surely SpeedStep (or CoolNQuiet) is a better solution than arbitrarily throttling the CPU?
If I throttle my CPU to 50%, thus doubling the battery life, but I’m doing something CPU-intensive, so that my task takes twice as long, then I’ll still get the same amount of work done before my battery gives out.
Yeah, I know my numbers don’t work. Is there anybody out there with reliable figures for the trade-off?
Surely SpeedStep (or CoolNQuiet) is a better solution than arbitrarily throttling the CPU?
Any modern laptop in the last 2 years already has SpeedStep / CoolNQuiet enabled. This is a constant, a default, it is always there – even for desktop systems. The power usage you see above is WITH that enabled. It’s standard.
Download CPU-Z and watch your CPU multiplier (and thus clock speed) change in real time with CPU load: http://www.cpuid.com/cpuz.php
If I throttle my CPU to 50%, thus doubling the battery life
This will only double your battery life if you’re actually at 100% CPU usage all the time. That would be… extraordinary, particularly on battery. For most use cases, your CPU will be idle the vast majority of the time.
The reason to throttle the CPU, as I said in the post, is to not have to worry about unusual peaks in CPU usage. Let’s say you happen to visit some web page with a horribly coded flash advertisement that uses 100% CPU time … do you want to watch task manager, see the unusual CPU usage, and manually close that web page? Or do you want the system to automagically throttle the web page’s CPU usage back to a reasonable level for you?
Also, understand that the CPU throttle does not actually disable a CPU core. A throttle of 50% means neither core can never be above 50% usage. Tasks will still be dispatched by whichever CPU core is available, so you get all the benefits of a dual-core chip, just a “slower” one.
Throttling is not always a clear win. According to the Intel Linux power optimization guys, the way to saving power is a race to idle. That is, when you have some work to do, the most efficient way is to do the work as fast you can and then turn off everything you can. By being able to influence the whole software infrastructure, open-source platforms can leverage this by coordinating wake-up times to take care of all the backgroundwork in a single power-up cycle. User unfriendly programs, such as flash advertisements, of course ruin this by breaking the premise that all the work to be done is actually useful. Ignoring this there are actually huge power reductions to be reaped in the x86 platform by coordinating sleepcycles. 99% of the time most of your laptop can be asleep, only the backlighting and minimal power to handle activity on wireless and input devices needs to be active.
Regarding LED backlights, they just need their time - current LEDs still aren’t significantly more efficient than cathode tubes. But given the trends, the tubes will be history soon.
But seriously, thanks for the highly informative article… I revisited the “The Cost of Leaving Your PC On” too, which has caused me to rethink my whole server-on-24/7/365 setup I got going.
Also, for some folks, myself included- lowering the brightness in the display for power consumption reduction is just not going to happen, for a number of reasons such related to their eyes. But not watching a DVD or graphics intensive application should become a no-brainer for non-intuitive users over time.
Would be interesting to see these stats with Aero turned off. Or at least the GPU one. I suppose the differences are small, but if one wants to save power then turning off Aero could give some extra time.
I like the way kubuntu handles my laptop. It generally throttles down to 800Mhz unless theres actually a high sustained usage (startup etc). This way you have the power if and when you need it. And it automatically dims the screen a bit when disconnected.
I find dual cores are alot more responsive even on low power, even including when I’m using eclipse, which uses a fair amount of resources.
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In all, none of our configurations consumed more than an additional watt moving from Vista’s Classic to Aero interface. Power consumption did spike by between 10 and 15W when using Aero’s 3D window switching feature, though. This spike didn’t last for much more than a second, so it’s unlikely to have a significant impact on overall system power consumption or noise levels. In fact, none of the cards we tested with variable-speed cooling fans even ramped up their fan speeds during our Aero testing.
I like the way kubuntu handles my laptop. It generally throttles down to 800Mhz unless theres actually a high sustained usage (startup etc). This way you have the power if and when you need it
To be clear, all modern operating systems do this-- heck, even ancient crusty old circa-2001 Windows XP does it. As long as you have a CPU built in the last 2-3 years which supports dynamic clock adjustment. It’s quite standard…
Honestly, there’s no point in using any sort of “power saver” mode. Processes that run will still run, but take longer to do so. If you have a process that takes 10s normally, and 20s with the CPUs throttled at 50%, what have you gained?
Of course, you need to have more fine-grained data to answer this question, but I have a feeling that the answer will be “not much”.
The only real result of using power savings mode is waiting longer for your computer to do the things you want it to do anyway, hence negating the power savings.
If you want to reduce CPU power consumption, run less processes.
@Mike:
That theory doesn’t necessarily work, because power is not consumed linearly based on increased work.
In addition, increasing the power consumed in the laptop has a net effect of increasing the heat generated, which will cause the fan to run longer, hence using more battery power.
Only wimps use Core 2 processors. Real men use Pentium 4s in their laptop. Real men have fried testicles
Humour apart, I’ve got a P4 Prescott with HT on my laptop. Do you think HT being turned on/off affect battery life? I’ve not been able to quantitatively measure, but would assume that with HT on, each hyper-thread is in a way throttled to 50%. Would this help battery life in the case of your horribly coded Flash ad?
As I mentioned above, I’d be interested to see some more data about this. From what I’ve seen, the power consumption for the different P-states is almost linear.
With CPUs that support something like Intel’s Speed Step technology, an explicit power mode setting isn’t very useful. You get low clock speeds when browsing the web, and the full attention of the CPU when, say, resizing that image or compiling.
(Yes, I use my ultra portable for software development on the go quite a lot)
I like the way kubuntu handles my laptop. It generally throttles down to 800Mhz unless theres actually a high sustained usage (startup etc). This way you have the power if and when you need it
To be clear, all modern operating systems do this-- heck, even ancient crusty old circa-2001 Windows XP does it. As long as you have a CPU built in the last 2-3 years which supports dynamic clock adjustment. It’s quite standard…
I think you misunderstood what he tried to say, the default behaviour with Windows is to increase clock frequency “immediately” (within a few milliseconds) to the maximum as soon as something uses 100% CPU (at least last time I checked, I always used SpeedSwitch XP to force the lowest speed in battery mode - the advanced settings never worked right for me), whereas under Linux you can configure things to e.g. only switch to the next higher clock frequency and only after at least 4 seconds of 80% CPU usage or similar things (though I have no idea what the default configuration for this is under Kubuntu).
This here should be a universal truth for all electrical devices (gadgets). I few times I have chatted to people who have recently got new phones, only to hear them complain about battery life.
I grab the little buggers, hit settings, and take the brightness down nice and low. As all phones I have seen default to 100% brightness. Note I have worked with a decent selection of handsets, as I did some mobile game porting straight out of Uni.
This was one of the 1st things I did to my SE k608i - cranked it straight down to 50%. I still get to 3-4 days battery life on the original battery. Probably one of the main reasons I have had the same phone for more than two years. While I don’t make a lot of calls, I do manage some games of solitaire in now and then.
The urban legend, that a LED backlit saves energy, is disproved with your measurings.
So why pay the extra fee for an LED-backlight than?
Only for the little savings in weight (which correlate with some mechanical instability)?
What about using the built-in speakers at various levels? I know for handheld games, you can extend the battery life quite a bit by using earbuds or turning the sound off/down.
