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I have a server that, as of the upgrade to 10.04, is now running the "ondemand" CPU scaling daemon. Why would it automatically install this? I don't want my server saving power at the expense of performance.

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3  
It's cold in my flat, too, so I want it to generate more heat, especially in the winter. –  A Student at a University Sep 9 '10 at 15:49
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You're mistaking the ondemand governor for the powersave one. –  Leon Nardella Sep 9 '10 at 22:42
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Agreed with Leon. Ondemand speeds up if there's something to do and slows down if it's idling. It does not restrict the CPU's ability to change speeds, but rather takes advantage of it. –  maco Sep 10 '10 at 0:15
    
Possible Duplicate askubuntu.com/questions/285434/… –  Qasim Jun 14 '13 at 14:58
    
It increases response times on a mostly idle server. –  A Student at a University Jul 3 at 11:50
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7 Answers

up vote 24 down vote accepted

Instead of disabling execution of the /etc/init.d/ondemand (as sugested by George) script you should use the this command

sudo update-rc.d ondemand disable

To make the init system not start the script, this is the recognized way of doing it! Disabling the exec permission (sudo chmod -x /etc/init.d/ondemand) might be overwritten if the package is updated.

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Frequency scaling isn't static. As soon as there is work to do, the CPU hops into action, P states boost up, and everything flies.

It's enabled because it's widely seen as a good thing. Saves you energy (good for your wallet and the environment). Keeps heat down (so important in a server room). And it's pretty unnoticeable.

Moreover on modern Intel chips, if you have scaling on you can use "turbo boost" where one core will run at higher-than-stock speeds for a time. This is very useful for spikes of single-threaded work. Without scaling enabled, you don't get this.

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How long does it take ondemand to scale up on a P4 Xeon? –  A Student at a University Sep 27 '11 at 13:45
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You could install the rcconf debian tool:

sudo apt-get install rcconf

then disable the "ondemand" service from there.

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I can't find any deprecation warning about the rcconf tool: you are missing the point and provided a completely wrong URL. I didn't mean Arch's way of configuring rc scripts, but rather the debian tool and that looks alive and well. –  Manuel Feb 6 '13 at 16:30
    
Thanks for pointing it out and supplying a helpful link! (I deleted my initial and wrong comment) –  nutty about natty Feb 6 '13 at 17:02
    
Also edited the original response! –  Manuel Feb 6 '13 at 18:24
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To make all CPUs run at maximum performance continually on a Ubuntu desktop or server, run:

sudo chmod -x /etc/init.d/ondemand

at the shell prompt and enter your password. This disables the shell script that makes all CPUs run at speed "OnDemand", making them default to full speed (Performance). You will need to reboot for this to take effect.

I have only tested this in Ubuntu Jaunty 9.04, but it should work and not cause any problems on any version of Ubuntu.

I think the Ubuntu defaults are strange for this. A desktop or server should run at full speed, in my opinion.

Regards, George

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I don't think it's strange. Whilst certainly mobile is the most critical scenario for power-saving, reducing power usage also means less fan noise in a desktop scenario, and less heat to deal with in a server room. Running constantly at maximum speed is a bit of a waste, only really necessary for rare cases where ondemand gets it wrong. –  bobince Sep 9 '10 at 18:33
    
@bobince - You are probably right, but for a desktop I have noticed that OnDemand gives a sluggish response compared to Performance, and I think the computer can still sleep properly with the above change. It should be an option in System/Administration or System/Preferences. –  George Gesslein II Sep 9 '10 at 20:36
    
Right, the only place this makes sense is on laptops where charge-time is shortened and battery-time extended by scaling the CPU. –  Source Lab Sep 9 '10 at 22:02
    
saving the environment, anyone?? –  nutty about natty Feb 3 '13 at 8:14
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On some systems, the 'ondemand' governor is unfortunately broken.

This is the case for "Intel(R) Core(TM)2 Quad CPU Q9300 @ 2.50GHz" and kernel 2.6.32-42.

The kernel thinks it can set the frequency individually for each CPU while the hardware actually only allows setting the frequency on groups of several CPUs (e.g. CPU 0 and 1 together, and CPU 2 and 3 together).

You may find out that the kernel isn't aware of this by looking at the /sys/devices/system/cpu/cpu*/cpufreq/affected_cpus files which contain "0", "1", "2", "3" instead of "0 1", "0 1", "2 3", "2 3".

The visible effect of this missmatch is a single-threaded process that starts running full speed on one CPU (the 'ondemand' governor reacts fast), and then, after about 20 seconds (depends on setting details), looses some of its speed.

The reason is the OS, with the 'ondemand' governor, periodically reapplies low freqs on the idle CPUs, not expecting that it will also implicitly change the freq of our busy CPU. It's not even visible when you look at /sys/devices/system/cpu/cpu*/cpufreq/*cur_freq or /proc/cpuinfo, the OS is just not aware of it!

So, on these systems the solution is to switch back to the simple 'performance' governor.

PS: In my case, running the CPUs constantly at their full freq didn't change anything concerning fan noise. I suppose when a CPU is idling, a lower or higher frequency will not have much impact on its power usage.

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I have a new processor AMD Athlon II X4 631 (Fusion processor for socket FM1) and it doesn't save any energy whatsoever (I looked it with energy meter)! I don't have a turbo core, so I don't need ondemand setting. Most new processors save enery by themselves.

When benchmarking, there is a little difference, in the range on 1-2%, when comparing ondemand and performance setting.

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Welcome to AskUbuntu! You may want to back up your statements with full statistics/research as your answer could be misunderstood as an opinion rather than a researched answer. –  Oyibo Nov 9 '12 at 12:32
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This is old, but since no one mentioned it, and for the sake of completeness, I will add that the argument how CPU which runs on the maximum speed will waste power, produce heat, fan noise etc. is WRONG.

Almost all modern CPUs, especially Desktop / Server CPUs, will enter deep sleep mode when idle (google race to idle.).

Voltage scaling will probably save more power, so on laptops this could increase running time a little, but on desktop and servers running performance governor will be fine for most of 'normal' users (who don't run server farms or similar.).

I use performance gov with my i7-2600k and the CPU temperature is usually around 30 C.

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