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From: Terry Lambert <terry@lambert.org>
Message-Id: <199607051905.MAA15231@phaeton.artisoft.com>
Subject: Re: Running SMP
To: peter@spinner.dialix.com (Peter Wemm)
Date: Fri, 5 Jul 1996 12:05:50 -0700 (MST)
Cc: erich@uruk.org, freebsd-smp@freebsd.org
In-Reply-To: <199607050157.JAA18293@spinner.DIALix.COM> from "Peter Wemm" at Jul 5, 96 09:57:40 am
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> > 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.

Actually, I got my (better than UP) numbers by increasing the
activation cycle for the kernel entrancy unlocking.

Basically, I ran the parallel make in an xterm window, then ...uh, then
set a textbook on the keypad enter key on the console keyboard.

8-) 8-) 8-).


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.