Date: Mon, 12 Feb 2001 16:22:37 -0800 From: Jordan Hubbard <jkh@winston.osd.bsdi.com> 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: <79723.982023757@winston.osd.bsdi.com> In-Reply-To: Message from Greg Lehey <grog@lemis.com> of "Tue, 13 Feb 2001 09:53:00 %2B1030." <20010213095300.D2178@wantadilla.lemis.com>
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> 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, I have measured that after a certain point make world *is* I/O bound and you can't really get any faster unless you do something to the I/O subsystem. We have several quad Xeons here, and back when I was more interested in measuring this sort of thing I found that I could get a "worldstone" time of around 37 minutes with -j8 and all 4 processors churning away. This was also during the exclusively BGL days of -current and things may scale slightly better or worse now, I dunno, but what I did find was that I could drop this all to something more like 23 minutes simply by putting /usr/src and /usr/obj into MFS (the machine I used also has a gigabyte of memory so this isn't difficult to do). That implies to me, at least, that after a certain point the CPU is going to be the bottleneck. - Jordan To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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