From: Con Kolivas <kernel@kolivas.org>
To: Nick Piggin <piggin@cyberone.com.au>
Subject: Re: [PATCH] O13int for interactivity
Date: Tue, 5 Aug 2003 13:06:38 +1000
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On Tue, 5 Aug 2003 12:21, Nick Piggin wrote:
> >I've already posted a better solution in O13.1
>
> No, this still special-cases the uninterruptible sleep. Why is this
> needed? What is being worked around? There is probably a way to
> attack the cause of the problem.

Sure I'm open to any and all ideas. Cpu hogs occasionally do significant I/O. 
Up until that time they have been only losing sleep_avg as they have spent no 
time sleeping; and this is what gives them a lower dynamic priority. During 
uninterruptible sleep all of a sudden they are seen as sleeping even though 
they are cpu hogs waiting on I/O. Witness the old standard, a kernel compile. 
The very first time you launch a make -j something, the higher the something, 
the longer all the jobs wait on I/O, the better the dynamic priority they 
get, which they shouldn't. 

No, this is not just a "fix the scheduler so you don't feel -j kernel 
compiles" as it happens with any cpu hog starving other tasks, and the longer 
the cpu hogs wait on I/O the worse it is.  This change causes a _massive_ 
improvement for that test case which usually brings the machine to a 
standstill the size of which is dependent on the number of cpu hogs and the 
size of their I/O wait. I don't think the latest incarnation should be a 
problem. In my limited testing I've not found any difference in throughput 
but I don't have a major testbed at my disposal, nor time to use one if it 
was offered which is why I requested more testing. 

Thoughts?

Con

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