On Sat, Oct 04, 2003 at 01:04:35PM -0700, Kris Kennaway wrote: > On Sat, Oct 04, 2003 at 03:20:03PM -0400, Richard Coleman wrote: > > 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. > > Yes, that's because (as discussed in the archives) the kernel treats > it like an extra, completely decoupled physical CPU and schedules > processes on it without further consideration. This is presumably the > cause of the slowdown, because it's only efficient to use the virtual > CPU under certain workload patterns. HTT is not magic performance > beans.
Right. And in addition it makes the system considerably more power hungry.. I measured both with and without SMP on my P4/2.4G HTT CPU. -- | / o / /_ _ [EMAIL PROTECTED] |/|/ / / /( (_) Bulte _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
