Messages in this thread | | | Date | Fri, 06 Jan 2006 10:13:16 +1100 | From | Peter Williams <> | Subject | Re: [PATCH] sched: Fix adverse effects of NFS client on interactive response |
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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
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