From owner-freebsd-smp Sat Nov 23 17:29:01 1996 Return-Path: owner-smp Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id RAA21793 for smp-outgoing; Sat, 23 Nov 1996 17:29:01 -0800 (PST) Received: from red.jnx.com (red.jnx.com [208.197.169.254]) by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id RAA21787 for ; Sat, 23 Nov 1996 17:28:57 -0800 (PST) Received: from chimp.jnx.com (chimp.jnx.com [208.197.169.246]) by red.jnx.com (8.8.3/8.8.3) with ESMTP id RAA20785; Sat, 23 Nov 1996 17:28:26 -0800 (PST) Received: (from tli@localhost) by chimp.jnx.com (8.7.6/8.7.3) id RAA28719; Sat, 23 Nov 1996 17:28:10 -0800 (PST) Date: Sat, 23 Nov 1996 17:28:10 -0800 (PST) Message-Id: <199611240128.RAA28719@chimp.jnx.com> From: Tony Li To: smp@csn.net (Steve Passe) Cc: freebsd-smp@freefall.freebsd.org, Peter Wemm In-reply-to: smp@csn.net's message of 24 Nov 96 00:43:09 GMT Subject: Re: SMP -current merge References: <199611232323.PAA02050@root.com> <199611240043.RAA20563@clem.systemsix.com> Sender: owner-smp@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk I have tested the times reported by "time make" against a stopwatch, and they are accurate to within 0.5 second. I was surprised to see increasingly better times beyond "-j 2". I guess this is from parallelism on the disk accesses, ie when both CPUs are waiting for disk IO on a particular object build, there is another they can work on if jobs > 2. The point of diminishing returns seems to be around 8 jobs. That's entirely consistent with the behavior of other SMP systems (e.g., Solbournes). The optimal point increases with your compute/IO ratio. For an 8 processor Solbourne, I normally used -j 11. Note that the -l flag to Gnu Make is what one would _like_ to use to insure a consistent load level. Unfortunately, it's implementation doesn't exhibit enough damping, so you get feast or famine. ;-( Tony