resources: how to limit process to max. 20% CPU usage

alesz · 03-30-2006, 04:03 AM

1) Is it possible on linux kernel to start a process, that will use maximum of. e.g. 20% CPU?
2) Is it possible to change the CPU usage when the process is already running?

3) What about I/O usage? The network usage can be well limited, but what about disk usage or pipe usage?

The reason I would like to do this is simple... to lower CPU temperature and tweak troughput.
Example: a long program compile, prelink, any other cron job, folding@home, ...

I know about process and thread priorities, but what about limitind to a fixed number? Do I have to load some additional kernel module? My kernel is 2.6.16-1.2069_FC5.

ilikejam · 03-30-2006, 06:37 AM

Hi.

I don't think any of this is possible. It's not exactly high on most people's priority list to make their processes run _slower_.
You might have more luck changing the CPU clock speed. That can be done via a userspace utility, the name of which escapes me.

Incidentally, why not just run at full speed all the time? Do you have overheating problems?

Dave

alesz · 03-30-2006, 06:51 AM

Overheating is one of problems too, since I like my computer to run healthy as well. I've installed silent cooling, but let the heat be different problem. E.g. on a notebook the problem persists, there's no way to make even idle job from turning on those loud ventilators.

I'd like to run one of my genetic algorithms, which it'd take about 14 days to finish. I don't like to run idle task, but if no other, I'll make it that way: "init.d + nice".

I've been thinking about this problem awhile now, but posted the question anyway, if anyone would tell me something interesting.

So the only way I could run a process under 20% CPU, it would be possible to check timers programmatically I guess...

The 2nd and 3rd questions from 1st post are left to some non-written kernel module I guess... Or am I wrong (wish I were...)?

ilikejam · 03-30-2006, 09:50 AM

Hi again.

You could run a watchdog script to pause and start the process. You could run it for one second out of five.

e.g.

Code:

#!/bin/bash
#Get the PID of the process
MYPID=`ps -u $USER | grep geneticAlg | awk '{ print $1 }'`
#Start and stop the process
while true; do kill -SIGSTOP $MYPID; sleep 4; kill -SIGCONT $MYPID; sleep 1; done

Should do the job.

Dave

alesz · 03-30-2006, 02:49 PM

Dave,

very nice answer for CPU usage, thanks. I didn't come up with the idea I could do it with signals, but now it seems very reasonable.

I run your script now, and renice my chess engine for generic algorithm to 19.

Since the engine is asked every 5sec for an answer to new question, the 5+1 sec. interval would be too long, so I modified the intervals to 0.5+0.1sec, script is as follows:

Code:

#!/bin/bash
#Get the PID of the process
MYPID=`ps -u $USER | grep qchess | awk '{ print $1 }'`
#renice engine
renice +19 $MYPID
#renice watchdog
renice +5 $$
#Start and stop the process
while true; do kill -SIGSTOP $MYPID; sleep 0.5; kill -SIGCONT $MYPID; sleep 0.1; done

That's it.

I hope now I'll be able to compile Kdevelop 3.4 and everything will run smoothly, but that's another story.