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If you have like... 10 cores... and you use Apache and your load average is always under 5.0...

Would it slow your site any if you lowered to 6 cores?

(assuming you never reached any spikes that hit 6.0 in load)

Specs: Xen, 10 Cores at 2.0GHz, CentOS 5 64bit, using "uptime" to find load averages.

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closed as not a real question by womble, mgorven, Ward, Lucas Kauffman, rnxrx Aug 23 '12 at 16:55

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1 Answer

Maybe.

The problem is that the load average is exactly that -- an average. Sure, over the course of a minute you never got above 5 processes in the run queue, but what about in a particular second or so? You might have big spikes and just never know it. If you don't care about small latency spikes, you might get away with it.

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@dav this is the main point - a 1-minute load average of 5 might be a constant, continuous load of five threads saturating five cores, but it might also be 10 threads saturating 10 cores for half a minute and idling for the other half. In the latter case, halving the number of cores would increase response times for your users by the factor of 2. –  the-wabbit Jul 1 '12 at 10:48
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