Message-ID: <3F2F8146.6030301@cyberone.com.au>
Date: Tue, 05 Aug 2003 20:04:54 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: Oliver Neukum <oliver@neukum.org>
CC: Con Kolivas <kernel@kolivas.org>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org, mingo@elte.hu,
       felipe_alfaro@linuxmail.org
Subject: Re: [PATCH] O13int for interactivity
References: <200308050207.18096.kernel@kolivas.org> <20030804230337.703de772.akpm@osdl.org> <200308051726.14501.kernel@kolivas.org> <200308051012.12951.oliver@neukum.org>
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Oliver Neukum wrote:

>Am Dienstag, 5. August 2003 09:26 schrieb Con Kolivas:
>
>>On Tue, 5 Aug 2003 16:03, Andrew Morton wrote:
>>
>>>We do prefer that TASK_UNINTERRUPTIBLE processes are woken promptly so they
>>>can submit more IO and go back to sleep.  Remember that we are artificially
>>>leaving the disk head idle in the expectation that the task will submit
>>>more I/O.  It's pretty sad if the CPU scheduler leaves the anticipated task
>>>in the doldrums for five milliseconds.
>>>
>>Indeed that has been on my mind. This change doesn't affect how long it takes 
>>to wake up. It simply prevents tasks from getting full interactive status 
>>during the period they are doing unint. sleep.
>>
>
>If you take that to its logical conclusion, such tasks should be woken
>immediately. Likewise, the io scheduler should be notified when you know
>that the task won't do io or will do other io, like waiting on character
>devices, go paging out or terminate.
>

I don't think that is the logical conclusion because you are balancing
against other things.

As for the io scheduler, no, there is a lot that can be done (including
waiting on character devs) before it is no longer worth keeping the disk
waiting. AS really doesn't care in the slightest what a process does
between submitting IOs*, what is important is simply its IO pattern.

* except exit which is an easy case of course.


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