Message-Id: <5.2.1.1.2.20060105143705.00be85c8@pop.gmx.net>
Date: Thu, 05 Jan 2006 15:31:17 +0100
To: Peter Williams <pwil3058@bigpond.net.au>
From: Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH] sched: Fix adverse effects of NFS client 
  on	interactive response
Cc: Helge Hafting <helgehaf@aitel.hist.no>,
       Trond Myklebust <trond.myklebust@fys.uio.no>,
       Ingo Molnar <mingo@elte.hu>, Con Kolivas <kernel@kolivas.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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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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