From owner-freebsd-questions@FreeBSD.ORG  Tue Nov 23 03:10:55 2004
Return-Path: <owner-freebsd-questions@FreeBSD.ORG>
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 8AE8216A4CE
	for <freebsd-questions@freebsd.org>;
	Tue, 23 Nov 2004 03:10:55 +0000 (GMT)
Received: from auk1.snu.ac.kr (auk1.snu.ac.kr [147.46.100.31])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 2348743D1F
	for <freebsd-questions@freebsd.org>;
	Tue, 23 Nov 2004 03:10:55 +0000 (GMT)
	(envelope-from spamrefuse@yahoo.com)
Received: from [147.46.44.181] (spamrefuse@yahoo.com) by 
          auk1.snu.ac.kr (Terrace Internet Messaging Server) 
          with ESMTP id 2004112311:59:37:114046.29903.2460478384
          for <freebsd-questions@freebsd.org>; 
          Tue, 23 Nov 2004 11:59:37 +0900 (KST) 
Message-ID: <41A2A7A2.3040102@yahoo.com>
Date: Tue, 23 Nov 2004 11:59:46 +0900
From: Rob <spamrefuse@yahoo.com>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.3) Gecko/20041113
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: FreeBSD <freebsd-questions@freebsd.org>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-TERRACE-SPAMMARK: YES-__TRSYS_LV__3 (SR:-3.78)           
 (SRN:SPAMROBOT) -----------------                               
Subject: make -j$n buildworld : use of -j investigated
X-BeenThere: freebsd-questions@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: User questions <freebsd-questions.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>,
	<mailto:freebsd-questions-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-questions>
List-Post: <mailto:freebsd-questions@freebsd.org>
List-Help: <mailto:freebsd-questions-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>,
	<mailto:freebsd-questions-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 23 Nov 2004 03:10:55 -0000


Hi,

I have tested following with FreeBSD 5.3-Stable.

On several different PCs I have used
    make -j$n buildworld
with $n ranging from 1 to 9.

Although people suggest "-j4" as optimal in general
case, I have come to a very different conclusion:

1) single CPU with enough RAM (2 GHz, 512 MB)
    there's no significant speed up in the range
    "-j1" to "-j9".
    So "-j1" is as good as "-j9".

2) single CPU with little RAM (333 MHz, 64 MB)
    speed slows down rapidly from "-j1" to "-j9",
    because of intensive swapping.
    So "-j1" performs best in this case.

3) dual CPU with enough RAM (2 x 800 MHz, 1GB)
    speed up by almost two from "-j1" to "-j2",
    but after that no noticeable speed up anymore.
    So "-j2" is as good as "-j9".

----------------------------------------

With these simple tests, I come to the conclusion that
"make -j$n buildworld" is best with n = number of CPUs.
Does that make sense?

Rob.