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To: erich@uruk.org
cc: freebsd-smp@freebsd.org
Subject: Re: Running SMP 
In-reply-to: Your message of "Thu, 04 Jul 1996 11:44:12 MST."
             <199607041844.LAA11426@uruk.org> 
Date: Fri, 05 Jul 1996 09:57:40 +0800
From: Peter Wemm <peter@spinner.dialix.com>
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>>>erich@uruk.org said:
> 
> After hacking the hard-coded base address of the APIC, I tried running
> some kernel compiles to see what kind of performance I was getting.
> 
> Frankly, it was pretty rotten.  Here's what I got (multiprocessor
> 150MHz Pentium Pro w/256K caches):
> 
>   FreeBSD SMP  1 CPU :      4:36
>                 -j 2 :      4:15
> 
>   FreeBSD SMP  2 CPU :      4:28
>                 -j 2 :      4:28
> 
> This was all compiling the SMP kernel with almost no devices.  I almost
> couldn't tell the other CPU was activated, except that "sysctl" told
> me in big bold letters that it was, and I kept getting kernel error
> messages about "calcru: negative time: ..." and such after doing it.
> 
> Linux-SMP would give me at least a 1.5x speedup with a full kernel spinlock
> and badly parallelized makefile.  What's the deal here?

Yes, the FreeBSD 'make -j' does nothing much.  I (and so does phk) use the 
NetBSD make, which truely does run parallel jobs.  However, the NetBSD 
make is no longer compatable with our Makefile tree since Jordan changed 
the obj dir stuff...  it can only be used on the kernel now....

If you use that, and set COPTS="-O -pipe" in /etc/make.conf, and use 
somewhere around 'make -j3', you should see up to 180% or so of the speed 
of the single-job make on a SMP kernel.

However, the single-job SMP kernel runs things slower than non-smp 
(probably because of the scheduling, which is partly worked around in the 
code that I have on my checked out copy of the source).  'make -j3' was 
between 130% and 150% of the speed of the uniprocessor, generic kernel 
though, even with our bogus scheduling.

Cheers,
-Peter