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SubjectRe: Overscheduling DOES happen with high web server load.
   Date: 	Thu, 6 May 1999 10:42:18 +1000
From: Richard Gooch <rgooch@atnf.csiro.au>

Indeed. As a separate question, we may wonder why so many
processes/threads are being used, and whether that number
could/should be reduced. Perhaps the server is doing something
silly. But that's an aside. Instead, I'd like to explore ways of
reducing the (already low) scheduler overhead.

No, it is more beneficial to find out why so many tasks are waking up
so much in the first place, _THIS_ is the bug.

This smells of galloping herd phenomenon to me. And my nose says it's
accept() in this case, and my nose further states that implementing
wake-one semantics in accept() might even make this part of the
profiling go away and increase our TCP server performance
dramatically. Several people have suggested this to me in private
discussions, and I was skeptical at first, but now I'm starting to
believe it.

This has nothing to do with how many threads are being used, it has to
do with threads getting woken up only to find they have no work to do,
which is the only way the run queues can grow large enough for these
sorts of user processes.

Later,
David S. Miller
davem@redhat.com

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