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

From: Nick Piggin
Date: Wed Jul 05 2006 - 13:39:15 EST


Ingo Molnar wrote:
* Peter Williams <pwil3058@xxxxxxxxxxxxxx> 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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