Message-Id: <5.2.0.9.2.20030626122539.00cea738@pop.gmx.net>
Date: Thu, 26 Jun 2003 12:39:54 +0200
To: Helge Hafting <helgehaf@aitel.hist.no>
From: Mike Galbraith <efault@gmx.de>
Subject: Re: O(1) scheduler & interactivity improvements
Cc: Bill Davidsen <davidsen@tmr.com>, linux-kernel@vger.kernel.org
In-Reply-To: <3EFAC408.4020106@aitel.hist.no>
References: <20030623164743.GB1184@hh.idb.hist.no>
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At 11:59 AM 6/26/2003 +0200, Helge Hafting wrote:
>Mike Galbraith wrote:
>
>>ponders obnoxious ($&#!...;) irman process_load...
>>Too many random sleeper tasks steadily becoming runnable can DoS lower 
>>priority tasks accidentally, but the irman process_load kind of DoS seems 
>>to indicate a very heavy favoritism toward cooperating threads.
>>It seems to me that any thread group who's members sleep longer than they 
>>run, and always has one member runnable is absolutely guaranteed to cause 
>>terminal DoS.  Even if there isn't _always_ a member runnable, waking a 
>>friend and waiting for him to do something seems like a very likely thing 
>>for threaded process to do, which gives the threaded process a huge 
>>advantage because the cumulative sleep_avg pool will become large simply 
>>because it's members spend a lot of time jabbering back and forth.
>
>How about _removing_ the io-wait bonus for waiting on pipes then?

That's been done.

>If you wait for disk io, someone else gets to use
>the cpu for their work.  So you get a boost for
>giving up your share of time, waiting
>for that slow device.
>
>But if you wait for a pipe, you wait for some other
>cpu hog to do the first part of _your_ work.
>I.e. nobody else benefitted from your waiting,
>so you don't get any boost either.
>
>This solves the problem of someone artifically
>dividing up a job, using token passing
>to get unfair priority.

For pipes.

         -Mike 

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