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To: freebsd-current@freebsd.org
References: <18328.45282.562906.708945@celery.zuhause.org>
From: Richard Todd <rmtodd@ichotolot.servalan.com>
Date: Thu, 24 Jan 2008 13:04:15 -0600
In-Reply-To: <servalan.mailinglist.fbsd-current/18328.45282.562906.708945@celery.zuhause.org>
	(Bruce Albrecht's message of "Thu, 24 Jan 2008 09:38:10 -0600")
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Subject: Re: Weird performance behaviour in 7.0
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Bruce Albrecht <bruce@zuhause.org> writes:

> This is my first Q6600 based system, and my first 7.0 system, and my
> first AMD-64 system and my first ZFS base system, and I'm seeing
> something really strange.  Every now and then, processes run really
> slowly, like at 1/600th (or worse) than it ought to, but it racks up
> the CPU time as though it's running full tilt.
>
> For example, I have this little test program that just does a tight
> loop, and most times, it takes about 3 seconds to complete, but right
> now, it's taking about 2000 seconds to complete. Right now, it's
> consistently running slow, but sometimes it will run slow, but I can
> terminate it and start another one which will run at normal speed.

This wouldn't by any chance be an Intel 965-chipset-based motherboard
with 4G or more of memory, would it?  Because there's an interesting
little bug in the BIOS on some of those boards which causes the
cache-control registers to incorrectly declare a chunk of main memory
as uncacheable.  This results in random slowdowns depending on whether
your process lands in the "bad" zone of memory or not.  See 
http://article.gmane.org/gmane.os.freebsd.stable/50135/ for more details.