Re: [LAU] Re: difference between realtime-kernel and low-latency-kernel?

On Thu, Oct 04, 2007 at 02:33:29PM +0200, Florian Schmidt wrote:
> On Thursday 04 October 2007, Jacob wrote:
> > Hi,
> >
> > On Thu, Oct 04, 2007 at 10:29:56AM +0200, Florian Schmidt wrote:
> > > [...]
> > > And yes, i consider it a bug that top and other software report the
> > > SCHED_FIFO prio as negative values. Where does that come from? Does the
> > > prio already get listed as negative in /proc? Or do they simply do it to
> > > separate the SCHED_FIFO threads from SCHED_OTHER threads? Anyways POSIX
> > > speaks of positive SCHED_FIFO prios in the range 1..99 afaik..
> >
> > Hmmm, POSIX talks about priorities in the range of
> > min .. max,
> > where
> > min = sched_get_priority_min(alg)
> > max = sched_get_priority_max(alg)
> > max - min >= 32, if alg == SCHED_FIFO or alg == SCHED_RR
> > and alg being the the scheduling algorithm (like SCHED_FIFO, ...)
> >
> > Under Linux (according to 'man sched_get_priority_min') the follwoing
> > ranges apply:
> > SCHED_FIFO : min = 1, max = 99
> > SCHED_RR : min = 1, max = 99
> > SCHED_OTHER : min = 0, max = 0
>
>
> Ok thanks for clearing this up :) So in principle there actually even might be
> partially (or only) negative prios for SCHED_FIFO processes.

I've wondered about this too. I haven't found anything in the Web and in
my (rather old) copy of O'Reillys "POSIX.4" book
explicitely requiering a positive value (ok, I only searched for 15 minutes),
and I do not have a copy of the current spec. But since
sched_get_priority_min/max(alg) return -1 if alg is invalid, I wouldn't
expect it.

Maybe someone with access to the current spec could clarify this? ;-)

Jacob
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Received on Thu Oct 4 16:15:03 2007