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SubjectRe: [PATCH] sched: Fix adverse effects of NFS client on interactive response
Mike Galbraith wrote:
> At 10:31 PM 1/5/2006 +1100, Peter Williams wrote:
>
>> Mike Galbraith wrote:
>>
>>> At 08:51 AM 1/5/2006 +1100, Peter Williams wrote:
>>>
>>>> I think that some of the harder to understand parts of the scheduler
>>>> code are actually attempts to overcome the undesirable effects (such
>>>> as those I've described) of inappropriately identifying tasks as
>>>> interactive. I think that it would have been better to attempt to
>>>> fix the inappropriate identifications rather than their effects and
>>>> I think the prudent use of TASK_NONINTERACTIVE is an important tool
>>>> for achieving this.
>>>
>>>
>>> IMHO, that's nothing but a cover for the weaknesses induced by using
>>> exclusively sleep time as an information source for the priority
>>> calculation. While this heuristic does work pretty darn well, it's
>>> easily fooled (intentionally or otherwise). The challenge is to find
>>> the right low cost informational component, and to stir it in at O(1).
>>
>>
>> TASK_NONINTERACTIVE helps in this regard, is no cost in the code where
>> it's used and probably decreases the costs in the scheduler code by
>> enabling some processing to be skipped. If by its judicious use the
>> heuristic is only fed interactive sleep data the heuristics accuracy
>> in identifying interactive tasks should be improved. It may also
>> allow the heuristic to be simplified.
>
>
> I disagree. You can nip and tuck all the bits of sleep time you want,
> and it'll just shift the lumpy spots around (btdt).

Yes, but there's a lot of (understandable) reluctance to do any major
rework of this part of the scheduler so we're stuck with nips and tucks
for the time being. This patch is a zero cost nip and tuck.

If the plugsched patches were included in -mm we could get wider testing
of alternative scheduling mechanisms. But I think it will take a lot of
testing of the new schedulers to allay fears that they may introduce new
problems of their own.

Peter
--
Peter Williams pwil3058@bigpond.net.au

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