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

[Nick Piggin <nickpiggin@yahoo.com.au>]

Ingo Molnar wrote:
> * Peter Williams <pwil3058@bigpond.net.au> wrote:

>>Of course, a comprehensive (as opposed to RT only) priority 
>>inheritance mechanism would make the "safe/unsafe to background" 
>>problem go away and make this patch very simple.  Any plans in that 
>>direction?
> 
> 
> that seems quite unlikely to happen. I think you are missing the biggest 
> issue: for RT, if the priority inheritance mechanism does not extend to 
> a given scheduling pattern it causes longer latencies, but no harm is 
> done otherwise. But for SCHED_BGND we'd have to make sure _every_ place 
> is priority-inversions safe - otherwise we risk a potential local DoS if 
> a task with a critical resource is backgrounded! That's plain impossible 
> to achieve.

Right. And it isn't just straightforward things like locks, but
any limited resource.

mempools and block device requests are two that come to mind.

-- 
SUSE Labs, Novell Inc.

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