Message-ID: <421E1AC1.1020901@nortel.com>
Date: Thu, 24 Feb 2005 12:19:45 -0600
From: Chris Friesen <cfriesen@nortel.com>
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To: "Chad N. Tindel" <chad@tindel.net>
CC: Mike Galbraith <EFAULT@gmx.de>, akpm@osdl.org,
       linux-kernel@vger.kernel.org
Subject: Re: Xterm Hangs - Possible scheduler defect?
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Chad N. Tindel wrote:

> 1.  Kernel preempts all.  There may be some hierarchy of kernel priorities
> too, but it isn't important here.
> 2.  SCHED_FIFO processes preempt all userspace applications.
> 3.  SCHED_RR.
> 4.  SCHED_OTHER.
> 
> Under no circumstances should any single CPU-bound userspace thread completely 
> hose a 64-way SMP box.
> 
> Can somebody educate me on why it is correct to do it any other way?

Low-latency userspace apps.  The audio guys, for instance, are trying to 
get latencies down to the 100us range.

If random kernel threads can preempt userspace at any time, they wreak 
havoc with latency as seen by userspace.

Chris
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