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I have a HP Pavilion Elite e9105f running Ubuntu 11.10 Linux 3.0.0-14-generic x86_64 with unmodified core system. When I try to run some io heavy command such us dmg2img, cp -r, the system becomes very unresponsive and it only functions normally when these commands finish. What could be the problem and how could I fix it?

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up vote 3 down vote accepted

When I try to run some io heavy command such

Well, this would be your problem. Running a heavy IO command will divert the majority of system resources to it, including CPU and the bandwidth availability between your system and hard drive. With that in mind, it only makes sense that your computer would be unresponsive.

I myself experience this often, usually with video rendering. You could try setting the affinity of the process to use only one or two cores. schedutils will do this on a Linux based system. You can set it using taskset: taskset -c 3,4 -p 13545

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But, isn't this situation rare? I'm expecting that when I copy large files, I can still chat on pidgin. But in my situation, pidgin freezes and becomes completely unusable as well as other programs. – xiamx Jan 2 '12 at 0:12
@xiamx You stated it yourself - Heavy IO. Using a command like that is going to use up a lot of resources, its expected. – Simon Sheehan Jan 2 '12 at 0:16

It's probably too late for a reply, but I'd guess it's memory management related. Linux uses virtual memory cached memory as I/O buffering memory. When doing massive I/O, the kernel gets bogged down allocating/deallocating pages in the virtual memory system. Watch /proc/meminfo for a large drop in "Dirty" (pages) corresponding to the pauses.

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