Re: [PATCH] sched: Add SCHED_BGND (background) scheduling policy

[Peter Williams <pwil3058@bigpond.net.au>]

Con Kolivas wrote:
> On Wednesday 05 July 2006 09:35, Peter Williams wrote:
> > Problem:
> >
> > There is a genuine need for the ability to put tasks in the background
> > (a la the SCHED_IDLEPRIO policy in Con Kolivas's -sc kernels) as is
> > evidenced by comments in LKML re a desire for SCHED_BATCH tasks
> > to run completely in the background.
> >
> > Solution:
> >
> > Of course, one option would have been to just modify SCHED_BATCH so
> > that tasks with that policy run completely in the background but there is a
> > genuine need for a non background batch policy so the solution adopted
> > is to implementa a new policy SCHED_BGND.
> >
> > SCHED_BATCH means that it's a normal process and should get a fair
> > share of the CPU in accordance with its "nice" setting but it is NOT an
> > interactive task and should NOT receive any of the special treatment
> > that a task that is adjudged to be interactive receives.  In particular,
> > it should always be moved to the expired array at the end of its time
> > slice as to do otherwise might result in CPU starvation for other tasks.
> >
> > SCHED_BGND means it's totally unimportant and should only be given the
> > CPU if no one else wants it OR if not giving it the CPU could lead to
> > priority inversion or starvation of other tasks due to this tasks holding
> > system resources.
>
> Could we just call it SCHED_IDLEPRIO since it's the same thing and there are 
> tools out there that already use this name?

I'm easy.  Which user space visible headers contain the definition? 
That's the only place that it matters.  When I was writing a program to 
use this feature, I couldn't find a header that defined any of the 
scheduler policies that was visible in user space (of course, that 
doesn't mean there isn't one - just that I couldn't find it).

Peter
PS Any programs that use SCHED_IDLEPRIO should work as long as its value 
is defined as 4.
--
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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