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Date: Sat, 4 Oct 2003 16:39:03 +0200 (CEST)
From: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
To: freebsd-hackers@freebsd.org
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Subject: Hyperthreading slowdown
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Hi

I installed FreeBSD 4.9RC1 on P4 3GHz with hyperthreading and I see
drastic slowdown when kernel with hyperthreading is booted. For example
program compilation took this time:

hyperthreading kernel,  make -j 1 --- 1:09
hyperthreading kernel,  make -j 2 --- 0:42
singlethreading kernel, make -j 1 --- 0:45
singlethreading kernel, make -j 2 --- 0:41

Compilation does very few system calls so when I compile with only one
process (-j 1), it should be as fast as with singlethreading kernel. Do
you have any idea why is it so slow?

Mikulas