Re: Real Time Runqueue

[Richard Gooch]

Mike Kravetz writes:
> As you may know, a few of us are experimenting with multi-runqueue
> scheduler implementations.  One area of concern is where to place
> realtime tasks.  It has been my assumption, that POSIX RT semantics
> require a specific ordering of tasks such as SCHED_FIFO and SCHED_RR.
> To accommodate this ordering, I further believe that the simplest
> solution is to ensure that all realtime tasks reside on the same
> runqueue.  In our MQ scheduler we have a separate runqueue for all
> realtime tasks.  The problem is that maintaining a separate realtime
> runqueue is a pain and results in some fairly complex/ugly code.
> 
> Since I'm not a realtime expert, I would like to ask if my assumption
> about strict ordering of RT tasks is accurate.  Also, is anyone aware
> of other ways to approach this problem?

Yes, strict ordering is required. Years ago I championed a separate
runqueue for RT tasks. Linus even said he liked the approach. I got
busy and never nursed it to inclusion. The patch is here:
ftp://ftp.atnf.csiro.au/pub/people/rgooch/linux/kernel-patches/v2.1/rtqueue-patch

				Regards,

					Richard....
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