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