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

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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                                   [email protected]

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