Optimizing for Fan Noise

The author makes a point that moving an application from one core to four might look good in benchmarks, but that it will peg all four cores and cause the fan to start running. I'd argue that that is precisely what you want, and that the operating system should provide a user-controlled mechanism to throttle the CPU back. That way, if you want raw performance, you can get it, but if you want a quiet computer and longer battery life you can get that as well. You _should_ engineer your software to use all available resources. It's the OS's job to divvy up those resources.<p>I know CPU throttling is possible on many notebooks in Linux. Do any Mac users out there know of such a feature in OS X?

<i>Doubling the speed of a program by moving from one to four cores is a win if you're looking at the raw benchmark numbers, but an overall loss in terms of computation per watt.</i><p>The first time I read this I didn't understand it, but the author has laid a trap here for the unwary reader in the word "doubling". If you can get 4x the performance using 4 cores the energy efficiency is the same or better, but if your program scales poorly and only gets 2x performance from 4 cores the energy efficiency is worse.

The way to measure this is not by fan speed, it's by power draw. To measure power draw, the most reliable way is to:<p>a) Make sure you can get your machine in a quiescent state (say, 5 minutes after bootup, all unnecessary background tasks and services are turned off).<p>b) Make sure ambient temperature is the same between runs.<p>c) Hook your computer up to a PDU with power usage monitoring built in.<p>d) Run automated tests, measuring power usage by the machine during the test. The automated part is important, because you want them to be fairly lengthy and also repeatable.<p>e) Compare results before and after. It's important to have a baseline for comparison so you know whether you're making progress or not.

Battery life is a fair optimization. Fan noise is a function of your fans. I have a quad-core i7, and when I max it out with 8 threads (it has HT), it does not make any noise. The stock cooler is nearly silent. My case has 140mm fans (!), and they don't make much noise either. They are even mounted via rubber hangers, so the vibration is not transfered to the case (same goes for the hard drives, although those are quite silent now too).<p>In addition to this, the computer is on the floor, not right next to my ears. So even if it were louder, it would still not annoy me.<p>So basically, I think your computer is broken if you can hear the fans. It's either designed wrong, or in the wrong position, or both.

Based on what I've seen in my experiences with building my own computers, the cause of fan noise in computers is not so much a necessary evil in our age of faster processing (old CPUs like the Pentium 4 ran hot as well), but rather a simple hardware problem due to the fact that many computer manufactures use cheap/noisy small stock fans. Replace a computer cooling systems with a slower-rotating larger diameter fan, and you will most likely have more airflow with less noise. Obviously that solution would be harder in space-constrained laptops, but I imagine with some clever engineering (ex. having large fans blow out the bottom of the computer) the designers could work out those issues if they really had the money and inclination to do so.

I completely agree with this article. If there is one thing I hate it is a program which makes my laptop's CPU fan start whirring like a jet engine. Usually with games this is because developers didn't properly program a FPS limiter, or else the game just uses a lot of alpha blending and graphical effects.<p>However, with modern processors just because they are fast that doesn't mean that programmers have to max out the processor and make it heat up. For example, I wrote an article a while back about how I increased performance in a 2D game and brought processor usage from 99% to 35% using a few graphical tricks such as trying to do alpha blending during the load (precalculated) rather than while rendering each frame:<p><a href="http://experimentgarden.blogspot.com/2009/08/sdl-tile-game-with-soft-shadows.html" rel="nofollow">http://experimentgarden.blogspot.com/2009/08/sdl-tile-game-w...</a>

Personally, I have optimised fan noise right out of all computers, aside from those in server closets, for years.

Computer noise is a function of hardware design. It's true that lower-power hardware is easier to cool, but on a laptop space constraints prevent you from implementing proper (quiet) cooling solutions. There, you really are trading performance against noise.<p>My homebuilt desktop is an overclocked 4GHz 8500 with a 4870 video card. It uses over 300W when pushed, but is still practically inaudible due to its water cooling and 250mm fan radiator tucked away in the corner under the desk.<p><a href="http://www.silentpcreview.com/" rel="nofollow">http://www.silentpcreview.com/</a> is an excellent resource for finding low-noise hardware and designs.

It's interesting that there appears to be a trade-off between using parallelism to reduce response time and optimizing for power usage, specifically in the use of redundant computations to avoid communication between nodes (as mentioned in the Guy Steele slides posted earlier.) Precomputing information a user might request is another potential power-waster that can be very good for responsiveness. My first reaction: man, I have enough environmental dilemmas in my life already! Will I have to turn on "high latency mode" in my applications just like I turn off my low-flow showerhead while I'm lathering up?

In the end, I took this as a discussion of thermal energy dissipation as it pertains to mobile devices. In other words, battery life.<p>My conclusion is that we need to vastly improve the energy density of batteries (or consider using carbon-based energy sources to power mobile devices).<p>Edit: Not sure why this is getting downvoted. The end of the article really does discuss mobile devices and energy dissipation - which I found to be the most critical part. Yes, the author ties it in together nicely with his anecdote of writing out code by hand. So in his day, you optimized for code length. Now, he advocates that we optimize for lower energy consumption. But I would instead, or in parallel, argue that mobile devices also simply have too little energy available to them.

Interestingly relevant in light of recent discussions as to whether or not the "no third-party background apps on the iPhone OS for sake of power conservation" policy is valid for the iPad.

My solution: A small wire shelf with foldable legs gets used as our laptop desk. The foldable legs allows our "desk" to be adjusted to two different heights to suit different user preferences. The wire shelving allows adequate airflow around the laptop. It never gets hot like it used to on a solid surface. This solution costs under $10 and can be implemented with one very brief shopping trip.

Use a CPU that does not require a fan. The 1 Mhz 6502 did not need a fan. The ARM, Apple A4, and others processors do not need fans. The problem is the Intel architecture has too many fans.