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I've noticed my computer gets sluggish when the load increases past 1 (ie, the first number after "load average:" from the "uptime" command).

Heavy-duty processes (like rsync) often raise the load above 1, even if I renice them lowest priority (+19). Renicing them helps a little, but not a lot.

Can I tell nice (or another program) to completely stop (kill -STOP) any +19 processes when the load increases over 1 (and resume when the load decreases to .75 or something)?

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migrated from stackoverflow.com Oct 21 '11 at 16:43

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load average doesn't mean particularly much... it's just the number of processes actively running in specific time intervals. A load of 1.0 doesn't mean the system's fully busy, just that there's at least 1 process running at all times. It could be 20 processes each running for 5% of the time. – Marc B Oct 21 '11 at 16:15
    
Oh, I know. I've seen load average go to 120 once (the system was completely unresponsive). Someone once told me this number indicated percentage of CPU used (with 120% possible because Unix fudges this the same way they fudge in "df"), but I now think that's not true. I've just personally noticed that my system gets sluggish when the load average goes to 1.50, for example. – barrycarter Oct 21 '11 at 16:48
up vote 1 down vote accepted

FreeBSD has IDLE process class - see rtprio(1) manual page - so you can assign IDLE priority to rsync so it won't get timeslices when there are normal processes active.

http://www.freebsd.org/cgi/man.cgi?query=rtprio&apropos=0&sektion=0&manpath=FreeBSD+8.2-RELEASE&arch=default&format=html

Linux has ionice(1) for CFQ io scheduler: http://linux.die.net/man/1/ionice Very similar concept, but for I/O.

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ionice is exactly what I needed, thanks! – barrycarter Nov 3 '11 at 14:49

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