Hi,
I have been encountering lots of heavy system cpu usage. It is sporadic, last for about 10 minutes, and brings everything else to crawl (latency of even typing characters into an editor or a terminal is painfully slow). My computer is an i7 quad, and all 8 logical cores fire at near 100% during these periods.
I can see the usage clearly with htop. The red bars in htop indicate system use (I have attached a screen shot for an example). However, as there is no process per se, I have no clue what is causing it.

Does any one know of any means to identify what could be causing this usage? It is something I have to fix as the computer becomes unusable periodically throughout the day. However, I have absolutely no clue where to begin. Could something in proc be helpful?

One thing to add, I am using the computer as a ltsp server on ubuntu, attaching to it using two thin clients. There is always heavy ethernet traffic through the second ethernet card. I don't know if this is related. However, I do think all this problem began when I installed the ltsp and switched to using a thin client.

-m

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When CPU usage disappears into a black hole it's (usually) not userspace that's the problem. First guess driver(s) - in interrupt context probably.
So that Ethernet card may just be a good place to start. Have a look at /proc/interrupts and the context switch rate - say vmstat.
Quite often you won't get (to see) relief until you unload the offending driver. Hunt and peck unfortunately.

Interesting. Thanks for the advice!
-m

As a final post on this one, I tried everything I could to figure this one out. I had various system monitors running all day long and whenever this prolonged 100% system usage came back, I tried to see what was going on. It was all for nothing. Nothing made sense.
In the end, I just installed the latest ubuntu release (i.e. going from 10:10 to 11:04). Problem completely solved! Not a single problem since re-install. God knows what it was in the 10:10 release that caused all the trouble. It could've been anything, but it did seem to be interacting with the ltsp server (no trouble occurred prior to switching to the ltsp setup).
-m