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SubjectRe: Busy-wait delay in qmail 1.03 after upgrading to Linux 2.6
On Tue, Jan 20, 2004 at 08:22:16PM +0100, Haakon Riiser wrote:
> [Manfred Spraul]
> > If a thread switch happens in the indicated line, then the reader will
> > loop, until it's timeslice expires - one full timeslice delay between
> > the two gettimeofday() calls.
>
> Exactly. But on 2.6, the delay between the two gettimeofday()
> calls are sometimes up to 300 ms, which is 300 timeslices in
> 2.6, right? I have never observed more than _one_ timeslice
> delay in 2.4.
>
> > Running the reader with nice -20 resulted in delays of 200-1000 ms for
> > each write call, nice 20 resulted in no slow calls. In both cases 100%
> > cpu load.
>
> But when the listener and the writer have the same nice value,
> how is it possible to have a delay of 300 ms? Both the writer
> and the listener are ready to run, so wouldn't a 300 ms delay
> mean that the listener was given the CPU 300 times in a row?

The scheduler can do this for you with its priority modification heuristics.

Try running a test with Nick's scheduler, and see how much your timings
change.

Also, there is a scheduling patch in -mm that's not in 2.6.1 that might
affect you also.
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