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From: Andrew Gallatin <gallatin@cs.duke.edu>
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Date: Thu, 5 Sep 2002 15:20:20 -0400 (EDT)
To: John Baldwin <jhb@FreeBSD.org>
Cc: freebsd-alpha@FreeBSD.org
Subject: RE: ithread preemption
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John Baldwin writes:
 > 
 > On 05-Sep-2002 Andrew Gallatin wrote:
 > > 
 > > I've forgotten -- What are the symptoms of ithread preemption causing
 > > troubles on alpha?
 > 
 > Hangs on SMP under load.
 > 
 > > I have one (probably dumb) idea: Is the ithread preemption code
 > > guaranteed to switch back to the preempted thread when the ithread
 > > completes or blocks?  And continue through to the end of the interrupt
 > > dispatch code, returning back to the palcode?
 > 
 > It is not guaranteed to do that.

What keeps you from (eventually) running out of kernel stack space
then, as the interrupts keep coming in?

Eg, would it help to keep a per-cpu (not per thread) interrupt nesting
count and refuse to do preemption if the interrupt nesting count
exceeds a small constant?

Drew

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