Date: Sat, 04 Oct 2003 15:20:03 -0400 From: Richard Coleman <richardcoleman@mindspring.com> To: Kris Kennaway <kris@obsecurity.org> Cc: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz> Subject: Re: Hyperthreading slowdown Message-ID: <3F7F1D63.2010703@mindspring.com> In-Reply-To: <20031004190251.GA60026@rot13.obsecurity.org> References: <Pine.LNX.4.58.0310041623250.6065@artax.karlin.mff.cuni.cz> <20031004190251.GA60026@rot13.obsecurity.org>
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Kris Kennaway wrote: > On Sat, Oct 04, 2003 at 04:39:03PM +0200, Mikulas Patocka wrote: >>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? > > Do you realise that hyperthreading != a secret extra CPU in your system? > > Kris I didn't see anywhere in the message where he implied that. To me, the interesting thing is that there is such a larger difference between the compile time for -j1 and -j2 when using hyperthreading as compared to the difference between -j1 and -j2 for a single threaded kernel. It's over a 50% slowdown. Richard Coleman
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