From owner-freebsd-questions Sat Aug 14 13: 4: 7 1999 Delivered-To: freebsd-questions@freebsd.org Received: from posgate.acis.com.au (posgate.acis.com.au [203.14.230.14]) by hub.freebsd.org (Postfix) with ESMTP id 949D314C26 for ; Sat, 14 Aug 1999 13:03:27 -0700 (PDT) (envelope-from andymac@bullseye.apana.org.au) Received: from bullseye.apana.org.au (uucp@localhost) by posgate.acis.com.au (8.9.2/8.9.2/Debian/GNU) with UUCP id GAA07380; Sun, 15 Aug 1999 06:01:09 +1000 (EST) Received: from bullseye.apana.org.au (central.apana.org.au [203.9.107.245]) by bullseye.apana.org.au (8.8.8/8.8.8) with SMTP id VAA18072; Sat, 14 Aug 1999 21:34:54 +1000 (EST) (envelope-from andymac@bullseye.apana.org.au) Date: Sat, 14 Aug 1999 21:33:45 +1000 (EST) From: Andrew MacIntyre To: Terence Kelly Cc: freebsd-questions@FreeBSD.ORG Subject: Re: big RAM & pthreads on FreeBSD In-Reply-To: Message-ID: X-X-Sender: andymac@bullseye.apana.org.au MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message