Date: Mon, 12 Feb 2001 15:27:52 -0800 From: Alfred Perlstein <bright@wintelcom.net> To: Greg Lehey <grog@lemis.com> Cc: Dag-Erling Smorgrav <des@ofug.org>, Danny Braniss <danny@cs.huji.ac.il>, Matt Dillon <dillon@earth.backplane.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: soft updates performance Message-ID: <20010212152752.N3274@fw.wintelcom.net> In-Reply-To: <20010213095300.D2178@wantadilla.lemis.com>; from grog@lemis.com on Tue, Feb 13, 2001 at 09:53:00AM %2B1030 References: <E14RurO-0000Zl-00@cs.huji.ac.il> <xzp7l2wc6v6.fsf@flood.ping.uio.no> <20010213095300.D2178@wantadilla.lemis.com>
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* Greg Lehey <grog@lemis.com> [010212 15:23] wrote: > On Monday, 12 February 2001 at 15:29:17 +0100, Dag-Erling Smorgrav wrote: > > Danny Braniss <danny@cs.huji.ac.il> writes: > >> i've been doing some experiments with vinum, and doing a make buildworld > >> (with obj on the same vinum) > >> without soft-updates ~ 1 hour > >> with soft-updates ~ 40 minutes > >> which is a bit better than 3% :-) > >> > >> what i can't figure out is why -j 4 didn't make any difference. > > > > Because your I/O system is already saturated. The point with -jNN is > > that one job can run while another is waiting for I/O to complete and > > vice versa, but as your CPU gets faster the time spent actually > > compiling etc. becomes insignificant next to the time spent doing I/O, > > and if you're already doing I/O as fast as you can there's no room for > > improvement. On a machine with a slower CPU or a faster I/O system, > > you'd see improvement. > > In fact, it's exactly the opposite. 'make world' is CPU-bound, so the > speed of the I/O system is irrelevant. If it were I/O bound, soft > updates *would* make a difference, because a number of unnecessary > writes would be eliminated. Actually compiles are pretty meta-data intensive, almost compiled program is composed of several .o files, without softupdates those .o files are expensive to create. Another thing is temp files for preprocessor output and assembler output, these can be reduced by using -pipe but without -pipe, each compile takes probably 3 file creations, 3 sync ops without softupdates. So basically, using softupdates along with -jN make actually does make a difference. -- -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org] "I have the heart of a child; I keep it in a jar on my desk." To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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