Date: Tue, 13 Feb 2001 09:53:00 +1030 From: Greg Lehey <grog@lemis.com> To: Dag-Erling Smorgrav <des@ofug.org> Cc: Danny Braniss <danny@cs.huji.ac.il>, Matt Dillon <dillon@earth.backplane.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: soft updates performance Message-ID: <20010213095300.D2178@wantadilla.lemis.com> In-Reply-To: <xzp7l2wc6v6.fsf@flood.ping.uio.no>; from des@ofug.org on Mon, Feb 12, 2001 at 03:29:17PM %2B0100 References: <E14RurO-0000Zl-00@cs.huji.ac.il> <xzp7l2wc6v6.fsf@flood.ping.uio.no>
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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. Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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