[gentoo-user] Per-process CPU % usage limit

[gentoo-user] Per-process CPU % usage limit

[Etaoin Shrdlu]

As the subject says, is there any way to force a particular process to 
use at most a given CPU percentage?

Ulimit does not help, since I don't want a CPU time limit and I don't 
want the process to be killed.

The problem is that some very CPU-consuming apps, even if started with 
the lowest priority (eg, nice -n 19), still eat up 100% CPU (with 
subsequent overheating, fan start, throttling, etc.) if the system is 
not busy and has nothing else to do. What I'd like to know is whether it 
is possible to impose such a CPU percentage usage limit.

Thanks for any help.
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Re: [gentoo-user] Per-process CPU % usage limit

[Richard Fish]

On 7/8/06, Etaoin Shrdlu <shrdlu@unlimitedmail.org> wrote:
> The problem is that some very CPU-consuming apps, even if started with
> the lowest priority (eg, nice -n 19), still eat up 100% CPU (with
> subsequent overheating, fan start, throttling, etc.) if the system is
> not busy and has nothing else to do. What I'd like to know is whether it
> is possible to impose such a CPU percentage usage limit.

Well, I would first upgrade my cooling fans so the processor couldn't
overheat! :-)

But you could also enable "CPU freqency scaling" in the kernel, with
the ondemand governor, and use the various settings in
/sys/devices/system/cpu/cpu0/cpufreq to control the clock speed and
behavior of the system.  You can use scaling_max_freq to specify the
maximum frequency of the processor so that it will not overheat or
throttle, no matter what the load is, and the
ondemand/ignore_nice_load setting will tell the governor not to
increase the clock speed for niced processes.

-Richard
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Re: [gentoo-user] Per-process CPU % usage limit

[Etaoin Shrdlu]

First, thanks for your answer!

On Saturday 8 July 2006 23:13, Richard Fish wrote:

> Well, I would first upgrade my cooling fans so the processor couldn't
> overheat! :-)

Upgrading cooling fan in a laptop isn't the easiest thing to do! :)

> But you could also enable "CPU freqency scaling" in the kernel, with
> the ondemand governor, and use the various settings in
> /sys/devices/system/cpu/cpu0/cpufreq to control the clock speed and
> behavior of the system.  You can use scaling_max_freq to specify the
> maximum frequency of the processor so that it will not overheat or
> throttle, no matter what the load is, and the
> ondemand/ignore_nice_load setting will tell the governor not to
> increase the clock speed for niced processes.

This is better, but still affects the system as a whole, and higly 
depends on the capabilities of your CPU.
What I really was looking for is something that can be configured 
per-process, to be able to limit only the CPU eaters.

Though not exactly what I was looking for, the ondemand/ignore_nice_load 
approach is probably the closest to what I want, although it still 
requires to be running at reduced CPU frequency. While certainly 
avoiding overheating, IIUC the governors.txt file all the system runs at 
reduced speed, but the CPU-intensive tasks (if suitably reniced) do not 
make the CPU increase its frequency. And we're still talking about CPU 
speed, not % usage.

I guess that truly limiting per-process CPU usage to a maximum percentage 
would require some modification to the kernel scheduuling code, After 
another bit of googling, I found this

http://www.tls-technologies.com/CPU/cpu-main.html

but unfortunately that is only for the 2.4 kernel.

Thanks for the answer,
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Re: [gentoo-user] Per-process CPU % usage limit

[Evan Klitzke]

On 7/8/06, Etaoin Shrdlu <shrdlu@unlimitedmail.org> wrote:
> As the subject says, is there any way to force a particular process to
> use at most a given CPU percentage?

Although I haven't used it myself, I am fairly confident that this is
what the cpu option does in /etc/security/limits.conf.  You will need
to have PAM enabled.

-- Evan Klitzke
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Re: [gentoo-user] Per-process CPU % usage limit

[Etaoin Shrdlu]

On Wednesday 12 July 2006 01:32, Evan Klitzke wrote:

> Although I haven't used it myself, I am fairly confident that this is
> what the cpu option does in /etc/security/limits.conf.  You will need
> to have PAM enabled.

The comments in the file talk about "CPU time (MIN)", so I guess this 
does the same as ulimit -t, and furthermore affects all of a given 
user's processes (not just a chosen process).
Anyway, I'll take a look.
Thanks for the info.
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