[CentOS] too much cpu system time with kernel 2.6.9-22.0.2.EL

Lamar Owen lowen at pari.edu
Thu Mar 9 18:24:15 UTC 2006

On Wednesday 08 March 2006 11:18, David Mansfield wrote:
> The system is slow, relatively (866Mhz cpu) and the network is fast
> (gigabit) so the limiting factor should be CPU.

What is the actual throughput on the GigE?  What KIND of GigE?  Which driver?

> However, at times, the system gets into a 'weird' state where instead of
> using about 85% user/ 15% system, it goes to 50% user and 50% system.

> Now 50% system time for this load is ridiculous, and as I said before,
> most of the time it is 85/15 and only occasionally get's 'stuck' in
> 50/50.

> CPU: CPU with timer interrupt, speed 0 MHz (estimated)
> Profiling through timer interrupt
> samples  %        symbol name
> 21117    36.5340  default_idle

> This is CRAZY! How can default_idle be sucking away cycles when the
> system is (should be) cpubound?

> Can anyone explain this?

GigE DMA, perhaps?

DMA time would show as cpu idle, I would think.

Bus contention between the GigE and the disk?  (Servers have split buses for a 
reason...and PCIe is a switched architecture for a reason)
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772

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