is context switching slow

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http://serverfault.com – I'm having high system CPU usage with high-load Apache server running. mpstat shows low %irq and %soft, but Apache spawns a lot of sub-processes, and I suspect context switches to be the reason of high sys% CPU usage. Am I right, and the high system CPU usage is caused by context switches, or I should debug it further? And if so, how do I debug it? (HowTos)