Re: miserable performance of 2.6.21 under network load

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Aaron Porter wrote:
	I'm in the process up upgrading a pool of apache servers from
2.6.17.8 to 2.6.21.5, and we're seeing a pretty major change in behavior.
Under identical network load, 2.6.21 has a load average more than 3 times
higher, cpu 0 spends well over 90% of its time in interrupts (vs ~30%
under 2.6.17). When we hit 3k apache sessions, ksoftirqd eats 100% of cpu0
and our network traffic drops off rapidly. The end result is that 2.6.17
performs twice as well under this load.
Is it always CPU 0, or does it move? Are you running irqbalance? If you're
running irqbalance, you can run a script that alternates between 'cat
/proc/interrupts' and 'mpstat -P ALL 5 10' and watch the offending interrupt
jump around between processors. It's not as informative as oprofile, as Andi
suggested, but it's really easy to set up.
	-- Chris
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