Re: Is timeslicing broken?

[Nick Garnett <nickg at ecoscentric dot com>]

Gary Thomas <gary@mlbassoc.com> writes:

> Nick Garnett wrote:
> > Gary Thomas <gary@mlbassoc.com> writes:
> >
> >> It seems that timeslicing of equal priority threads is broken
> >> in the presence of any other higher priority threads that may
> >> cause preemption.
> >>
> >> I have modified the timeslice test to have an additional thread.
> >> This thread is higher priority than the "worker" threads and
> >> all it does is wake up at a modest frequency (every 2 ticks).
> >> What this does is to preempt one of the worker threads before
> >> it has a chance to run the timeslice timer down to zero.  When
> >> the worker thread is resumed, the timeslice timer is reset and
> >> the same worker thread continues running forever, never being
> >> rescheduled and letting the other worker threads run.
> >>
> > As it happens, I also fixed this bug myself a few weeks ago. It has
> > been running in our test farm for a while. I think my patch is a
> > little more complete since it also deals with the bitmap scheduler and
> > kapidata.h. I also think it leaves the scheduler code a little tidier.
> > Anyway here it is:
> 
> Obviously cleaner since you're more familiar with the various C++ classes,
> etc. within the scheduler.
> 
> Why aren't your functions (and the layout, etc) protected by
> CYGSEM_KERNEL_SCHED_TIMESLICE?  Does it still build/run with this CDL
> option disabled?

I chose to arrange the headers and the bitmap scheduler to always have
these functions defined. Where they are non-functional they are just
empty inlines. I did this so that the ifdefs can be removed from the
main code, which I think makes it cleaner and easier to read, and is
more in keeping with the sort of approach one should take with C++.

I've tested it by hand with timeslicing disabled and with the bitmap
scheduler enabled. It has also been through the various config
permutations in the test farm, so I am fairly confident that it is
robust.

> 
> Query: did you also write the timeslice2 test?  It looks a lot like
> mine (cleaner - I didn't spend a lot of time on it)?  Obviously great
> minds think alike :-)

I did write it, it was the obvious thing to do after all :-)


If you are happy for me to do so, then I'll check this patch in.


-- 
Nick Garnett                                     eCos Kernel Architect
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