It was shown earlier in the thread that no thundering herd occured
in the test, because apache serializes the accept with a lock.
There is no global consensus of this fact. Apache may be using flock
to serialize, but nobody has stated that flock does not present the
same problem on the kernel side (everyone waking up and fighting for
the flock, one winning and everyone else going back to sleep).
The scheduling rate is absurd, and so are the run queue lengths which
must be leading to this behavior. I am willing to be proven
otherwise, but my reading of the data is still galloping herd.
Someone could put this to rest by implementing a quick profiling hack
in the kernel, do something similar to what the timer based profiling
in the kernel does already, but instead record profiling ticks for
calls to the scheduler and record the tick for who it is that called
the scheduler (essentially you're profiling the WCHAN).
Data produced from this during one of these tests would prove
extremely useful.
Later,
David S. Miller
davem@redhat.com
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