Re: [PATCH] sched: Fix adverse effects of NFS client on interactive response

[Mike Galbraith <efault@gmx.de>]

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).

        -Mike 

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