Limiting certain processes to CPU % - Linux

Question

I have the following problem: some processes, generated dynamically, have a tendency to eat 100% of CPU. I would like to limit all the process matching some criterion (e.g. process name) to a certain amount of CPU percentage.

The specific problem I'm trying to solve is harnessing folding@home worker processes. The best solution I could think of is a perl script that's executed periodically and uses the cpulimit utility to limit the processes (if you're interested in more details, check this blog post). It works, but it's a hack :/

Any ideas? I would like to leave the handling of processes to the OS :)

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Thanks again for the suggestions, but we're still missing the point :)

The "slowDown" solution is essentially what the "cpulimit" utility does. I still have to take care about what processes to slow down, kill the "slowDown" process once the worker process is finished and start new ones for new worker processes. It's precisely what I did with the Perl script and a cron job.

The main problem is that I don't know beforehand what processes to limit. They are generated dynamically.

Maybe there's a way to limit all the processes of one user to a certain amount of CPU percentage? I already set up a user for executing the folding@home jobs, hoping that i could limit him with the /etc/security/limits.conf file. But the nearest I could get there is the total CPU time per user...

It would be cool if to have something that enables you to say: "The sum of all CPU % usage of this user's processes cannot exceed 50%". And then let the processes fight for that 50% of CPU regarding to their priorities...

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Guys, thanks for your suggestions, but it's not about priorities - I want to limit the CPU % even when there's plenty of CPU time available. The processes are already low priority, so they don't cause any performance issues.

I would just like to prevent the CPU from running on 100% for extended periods...

Answer 1

Why limit the percentage of CPU when you can just adjust the priority of the process using renice? Using renice, and setting a low priority allows the process to still use 100% of the processor if it's available, but any other process with higher priority will get the process when it needs it, with almost no noticeable lag.

Answer 2

I don't remember and dont think there was something like this in the unix scheduler. You need a little program which controls the other process and does the following:

loop
    wait for some time tR
    send SIGSTOP to the process you want to be scheduled
    wait for some time tP
    send SIGCONT to the process.
loopEnd

the ratio tR/tP controls the cpu load.

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Here is a little proof of concept. "busy" is the program which uses up your cpu time and which you want to be slowed-down by "slowDown":

> cat > busy.c:
    main() { while (1) {}; }

> cc -o busy busy.c
> busy &
> top

Tasks: 192 total,   3 running, 189 sleeping,   0 stopped,   0 zombie
Cpu(s): 76.9% us,  6.6% sy,  0.0% ni, 11.9% id,  4.5% wa,  0.0% hi,  0.0% si
Mem:   6139696k total,  6114488k used,    25208k free,   115760k buffers
Swap:  9765368k total,  1606096k used,  8159272k free,  2620712k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
26539 cg        25   0  2416  292  220 R 90.0  0.0   3:25.79 busy
...

> cat > slowDown
while true; do
 kill -s SIGSTOP $1
 sleep 0.1
 kill -s SIGCONT $1
 sleep 0.1
done

> chmod +x slowDown
> slowDown 26539 &
> top
Tasks: 200 total,   4 running, 192 sleeping,   4 stopped,   0 zombie
Cpu(s): 48.5% us, 19.4% sy,  0.0% ni, 20.2% id,  9.8% wa,  0.2% hi,  2.0% si
Mem:   6139696k total,  6115376k used,    24320k free,    96676k buffers
Swap:  9765368k total,  1606096k used,  8159272k free,  2639796k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
26539 cg        16   0  2416  292  220 T 49.7  0.0   6:00.98 busy
...

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ok, that script needs some more work (for example, to care for being INTR-upted and let the controlled process continue in case it was stopped at that moment), but you get the point. I would also write that little script in C or similar and compute the cpu ratio from a comand line argument....

regards

Answer 3

Using cgroups' cpu.shares does nothing that a nice value wouldn't do. It sounds like you want to actually throttle the processes, which can definitely be done.

You will need to use a script or two, and/or edit /etc/cgconfig.conf to define the parameters you want.

Specifically, you want to edit the values cpu.cfs_period_us and cpu.cfs_quota_us. The process will then be allowed to run for cpu.cfs_quota_us microseconds per cpu.cfs_period_us microseconds.

For example:

If cpu.cfs_period_us = 50000 and cpu.cfs_quota_us = 10000 then the process will receive 20% of the CPU time maximum, no matter what else is going on.

In this screenshot I have given the process 2% of CPU time:

As far as the process is concerned it is running at 100%.

Settings cpu.shares on the other hand can and will still use 100% of the idle CPU time.

In this similar example I have given the process cpu.shares = 100 (of 1024):

As you can see the process is still consuming all the idle CPU time.

References:

http://manpages.ubuntu.com/manpages/precise/man5/cgconfig.conf.5.html http://kennystechtalk.blogspot.co.uk/2015/04/throttling-cpu-usage-with-linux-cgroups.html

Answer 4

PS + GREP + NICE

Answer 5

I dont really see why you want to limit the CPU time... you should limit the total load on that machine, and the load is determined by IO operations mostly . Ex: if i create a while(1){} loop, it will get the total load to 1.0, but if this loop does some disk writes the load jumps to 2.0... 4.0. And that's what killing your machine, not the CPU usage. The CPU usage can be easily handled by nice/renice.

Anyways, you could make a script that does a 'kill -SIGSTOP PID' for a specific PID, when the load gets too high, and kill -SIGCONT when everything gets back to normal... The PID's can be determined by using the 'px aux' command, because i see that it displays the CPU usage, and you should be able to sort the list using that column. I think this the whole thing could be done in bash...

Answer 6

The nice command will probably help.