Date: Sat, 14 Aug 1999 21:33:45 +1000 (EST) From: Andrew MacIntyre <andymac@bullseye.apana.org.au> To: Terence Kelly <tpkelly@eecs.umich.edu> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: big RAM & pthreads on FreeBSD Message-ID: <Pine.OS2.3.95.990814210636.388B-100000@CENTRAL> In-Reply-To: <Pine.GSU.4.05.9908112000270.23952-100000@krusty.eecs.umich.edu>
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On Wed, 11 Aug 1999, Terence Kelly wrote:
> I'm considering replacing Linux with FreeBSD on a
> computer I use, but first I have a few questions.
> (I searched the man pages and FAQ available at
> your Web site, but didn't find answers.)
I've not seen any responses to your query. I don't have a detailed
knowledge of your areas of interest, so take what I say with a shovelfull
of salt...
> 1. My 4-CPU machine has 2 GB of RAM. Does the
> latest stable SMP kernel support that much
> memory? In other words, can a single
> user-level process access all of that RAM?
> (I write memory-intensive simulation code
> and I can't afford to page/swap.)
It is my understanding that stock 3.2S is only known to work up to 1GB.
ISTR David Greenman noting that -current was good for 2GB and, with
patches 4GB. You may want to check the vital statistics for ftp.cdrom.com
as it is running a recent stock 3.2S build. You could try searching the
archives of the freebsd-stable mailing list for more info.
FreeBSD actively tries to keep pages in memory, and doesn't swap unless it
has to. This notwithstanding, I gather that it is prudent to make sure
that your available swap space is slightly largely than the available
memory, even if it will never actually get used.
> 2. Does the SMP kernel support multithreading
> in roughly the same way as Solaris, Linux,
> etc. via POSIX threads? I'm accustomed to
> a programming model in which the OS
> automagically assigns pthreads to processors
> and the threads run concurrently. My pthreaded
> code does what I expect on IRIX, Solaris, and
> Linux. Will I get the same general behavior
> from FreeBSD?
My understanding is that FreeBSD's SMP implementation isn't as advanced
as Linux's, let alone the commercial OSes. People are working to advance
the state of SMP, but in the -current environment only. I vaguely recall
a recent thread on this issue, with the upshot apparently being that the
current SMP infrastructure doesn't schedule pthreads on different CPUs;
they're scheduled on the CPU running the current process. You may want to
search the archives of the freebsd-smp mailing list to cross-check.
--
Andrew I MacIntyre "These thoughts are mine alone..."
E-mail: andrew.macintyre@aba.gov.au (work) | Snail: PO Box 370
andymac@bullseye.apana.org.au (play) | Belconnen ACT 2616
Fido: Andrew MacIntyre, 3:620/243.18 | Australia
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