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Date: Sun, 18 Dec 2011 00:00:15 +0200
From: Andriy Gapon <avg@FreeBSD.org>
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To: Adrian Chadd <adrian@FreeBSD.org>
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Cc: George Mitchell <george+freebsd@m5p.com>, freebsd-stable@FreeBSD.org,
	Oliver Pinter <oliver.pntr@gmail.com>
Subject: Re: SCHED_ULE should not be the default
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on 17/12/2011 23:20 Adrian Chadd said the following:
> Erm, just as a random question - since device drivers (and GEOM) run
> as separate threads, has anyone looked into what kind of effects the
> scheduler has on these?
> 
> I definitely have measurable throughput/responsiveness differences
> between ULE and 4BSD (and preempt/non-preempt on 4BSD) on my MIPS
> boards when they're bridging traffic. I wonder if there's something
> strange going on with the scheduling and preemption of driver netisrs,
> taskqueues, the fast interrupt handlers, etc.
> 
> This may -not- be a userland specific problem..

That's an interesting idea.  From the recent discussion about USB I can conclude
that USB threads run at higher priority than GEOM threads: PI_NET/PI_DISK vs
PRIBIO.  The former is from the ithread range, the latter is from the regular
kernel range.  Maybe it would make sense to give the GEOM threads a priority
from the ithread range too - given their role and importance.

-- 
Andriy Gapon