Weird performance behaviour in 7.0

Richard Todd rmtodd at
Thu Jan 24 11:38:36 PST 2008

Bruce Albrecht <bruce at> 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 for more details. 

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