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Date: Tue, 03 Oct 2006 23:38:28 -0600
From: Scott Long <scottl@samsco.org>
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To: David G Lawrence <dg@dglawrence.com>
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Cc: freebsd-stable@freebsd.org,
	John Marshall <John.Marshall@riverwillow.com.au>
Subject: Re: Watchdog Timeout - bge devices
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David G Lawrence wrote:
>> Very interesting data point.  I wonder if this accounts for some of the
>> inconsistency in the reporting from others.  In any case, SCHED_ULE is
>> still considered to be highly experimental.  Hopefully it will get some
>> more attention in the near future to bring it closer to production
>> quality.
> 
>    I'm not using SCHED_ULE on any of the machines that I'm seeing the
> timeout problem with em and fxp devices. I suspect the problem has to do
> with interrupt thread scheduling; maybe SCHED_ULE just somehow makes the
> problem worse?
> 
> -DG
> 

Well, the two things that will block the scheduler are critical sections
and spinlocks.  The system will complain about spinlocks that are held 
too long, but you might need WITNESS and/or INVARIANTS enabled for it.
Critical section debugging is almost non-existant; the only way to do it
is to turn on KTR and then feed the output to schedgraph.py.  This only
works reliably for UP, though.

Scott