CPU limits

Inspired by the recent posting of "FAQ 8.39 How do I set CPU limits?",
I hoped to solve this problem, that I always had with computationally
intensive scripts - namely that the CPU usage goes to 100%, and a very
noisy fan starts.
I'd much prefer to be able to set my script's CPU usage at - say - 75%
or similar...

In the FAQ I saw that this possibility is in the BSD::Resource module,
but unfortunately I work in Linux.
Moreover, I'm not certain that even under BSD this could be possible:
setrlimit seems to allow you just to kill processes going beyond your
given threshold.

Any hint?


Thanks!

Alessandro Magni

Re: CPU limits

Post removed (X-No-Archive: yes)

Re: CPU limits

"alexxx.magni@gmail.com" wrote:
> Inspired by the recent posting of "FAQ 8.39 How do I set CPU limits?",
> I hoped to solve this problem, that I always had with computationally
> intensive scripts - namely that the CPU usage goes to 100%, and a very
> noisy fan starts.
> I'd much prefer to be able to set my script's CPU usage at - say - 75%
> or similar...
>
> In the FAQ I saw that this possibility is in the BSD::Resource module,
> but unfortunately I work in Linux.

BSD::Resource works under Linux. Or at least some (I expect all or most)
parts of it do. So I don't think that that is a problem.

> Moreover, I'm not certain that even under BSD this could be possible:
> setrlimit seems to allow you just to kill processes going beyond your
> given threshold.

Yes, that is the problem. I don't know of any facility on any OS that does
this (but I haven't looked very hard.) I guess you could write a
baby-sitter process which goes into a loop where it sleeps for 3N
microseconds, then issues a kill STOP to your real process, then sleeps for
N microseconds, then issues a kill CONT to your real process. That should
restrict it to 75% CPU time. If your main program uses other types of
signals, this might not work very well.

Xho

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Re: CPU limits

On Nov 7, 11:40 am, "alexxx.ma...@gmail.com"
wrote:
> Inspired by the recent posting of "FAQ 8.39 How do I set CPU limits?",
> I hoped to solve this problem, that I always had with computationally
> intensive scripts - namely that the CPU usage goes to 100%, and a very
> noisy fan starts.
> I'd much prefer to be able to set my script's CPU usage at - say - 75%
> or similar...
>
> In the FAQ I saw that this possibility is in the BSD::Resource module,
> but unfortunately I work in Linux.
> Moreover, I'm not certain that even under BSD this could be possible:
> setrlimit seems to allow you just to kill processes going beyond your
> given threshold.
>
> Any hint?
>
> Thanks!
>
> Alessandro Magni

you can use BSD::Resource on linux.
or try this script :

#!/usr/bin/perl
#Description: These subs allow you control how much % CPU maximum
will use your script. CPU_start() must be called once when you script
start.
#This example script will use 30% CPU until Ctrl-C pressed:

CPU_start(); CPU_max(30) while 1;

use Time::HiRes qw(time);

sub CPU_used {
(map {$_->[13]+$_->[14]}
[split " ", Cat("/proc/self/stat")])[0]
}

{ my %start = (tm => 0, cpu => 0);
sub CPU_start { @start{"tm","cpu"} = (time(),CPU_used()) }
sub CPU_max {
my ($max, $real, $cpu) = ($_[0], time()-$start{tm},
CPU_used()-$start{cpu});
return unless defined($max) and $max > 0;
&sleep( $cpu/$max-$real );
}}

#
# macro used from CPU_used() and CPU_max()
#

sub sleep { select undef,undef,undef,$_[0] }
sub Cat {
local *F;
open F, "< ".$_[0] or return;
local $/ unless wantarray;
return ;
}


zaher el siddik
http://www.unixshells.nl/

Re: CPU limits

Quoth "alexxx.magni@gmail.com" :
> Inspired by the recent posting of "FAQ 8.39 How do I set CPU limits?",
> I hoped to solve this problem, that I always had with computationally
> intensive scripts - namely that the CPU usage goes to 100%, and a very
> noisy fan starts.
> I'd much prefer to be able to set my script's CPU usage at - say - 75%
> or similar...
>
> In the FAQ I saw that this possibility is in the BSD::Resource module,
> but unfortunately I work in Linux.

As others have mentioned, BSD::Resource works perfectly well under
Linux.

> Moreover, I'm not certain that even under BSD this could be possible:
> setrlimit seems to allow you just to kill processes going beyond your
> given threshold.

setrlimit sends a trappable signal when you reach your soft limit. The
problem is there is no rlimit for 'percentage of CPU used': I'm not even
sure it's a terribly well-defined property. Apart from anything else,
you don't really want your script to be using 75% CPU; you just want the
CPU to be 25% idle. Have you looked to see if there is some ACPI stuff
you could use to request this? I remember reading about some 'laptop
mode' for Linux which cut down the amount of CPU time available to
preserve power.

Ben

Re: CPU limits

On Nov 7, 11:10 am, all mail refused
wrote:
> On 2007-11-07, alexxx.ma...@gmail.com wrote:

> You should be able to use BSD::Resource on linux to get at
> the ulimit and setrlimit() sort of stuff. This can limit
> total CPU usage of a program - killing it when exceeded.
>
> If you want to ration CPU usage to some fraction of the total,
> or to a certain one of several CPUs etc that's a different
> question that I don't know the answer to.

You can use a VM and assign only one of the CPU's to the VM :)

Regards,
Ivan Novick
http://www.0x4849.net