Date: Thu, 4 Jul 1996 13:13:28 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: erich@uruk.org Cc: freebsd-smp@freebsd.org Subject: Re: Running SMP Message-ID: <199607042013.NAA13471@phaeton.artisoft.com> In-Reply-To: <199607041844.LAA11426@uruk.org> from "erich@uruk.org" at Jul 4, 96 11:44:12 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? There is a scheduler bug in the current SMP code which causes there to be an interspersal problem exiting the kernel as a scheduled entity. You can best see this by starting a kernel build on a remote system in an xterm, and then hitting return on the console. The scheduling is interleaved, and the console will be on the second processor, and the system will toggle between them. This is quite broken, and it should be ovious from the original patches I sent you that this is an attempt to preserve cache locality (the Jack Vogel patches lost cache locality by anonymously scheduling processes without regard to "preferred processor"). Any input you have on how to correct this would be welcome; I've beem dealing with Lite2 integration and porting issues, and wanted to ignore the scheduler and page mapping if I could. 8-). If not, I'm sure Peter or Poul or one of the others will get to it (or you could), before I have a chance. I have a PPC milestone commitment coming due soon, or I'd jump on it. 8-(. Regards, Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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