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SubjectRe: Overscheduling DOES happen with high web server load.
On Fri, 7 May 1999, Greg Lindahl wrote:

>Why is schedule called so frequently? The thundering herd. You get a
>new connection, everyone wakes up, only one gets work, and everyone
^^^^^^^^^^^^^^^^^^ wrong
>else goes back to sleep, each causing O(A) work to reschedule. M hits

The reality until 2.2.7 is that everyone wakes up, need_resched of the
current task is set to 1 so the rescheduled CPU will issue a schedule()
very shortly, but nobody of the wakenup tasks gets rescheduled and
schedule() become a nono. This is the main wastage of resources. I think
it's just fixed in pre-2.2.8-4 though ;).

Andrea Arcangeli


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