Date: Thu, 8 Nov 2001 20:16:34 -0600 From: Mike Meyer <mwm@mired.org> To: "Joesh Juphland" <part_lion@hotmail.com> Cc: hackers@freebsd.org Subject: Re: processor recommendations for multi-user freeBSD system ? Message-ID: <15339.15490.867966.409693@guru.mired.org> In-Reply-To: <F101y8VBDUfdfdhNzW30000d248@hotmail.com> References: <F101y8VBDUfdfdhNzW30000d248@hotmail.com>
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Joesh Juphland <part_lion@hotmail.com> types: > I am planning on building a true multi-user system (as opposed to a NFS > server, or a web server, or a mail server) - many people with many shells > will be doing many things. > > Two things have been decided: > > - it will run freeBSD > - it will be dual processor Why the dual processor requirement? There are lockups in the SMP kernel that don't exist in the UP kernel. A number of people have reported reliable reproduction of them, but nobody has fixed them. I don't know if there is a PR on it or not. > So what two processors should I use ? Coming from a Sun hardware > background, I originally thought to use PIII Xeons .. since they have a lot > of cache, and fast cache. I was thinking 512meg cache p3 xeons running at > 550mhz. > > But what about a modern athlon MP processor ? Much less cache, but it runs > at 266mhz, and it is much faster ... 1700mhz or so. I just traded - due to hardware failure - a dual PII/Xeon system for a 1GHz Athlon UP system. The Xeons had a 100MHz FSB with 256 meg of ram. The Athlon has a 266MHz FSB with 256 meg of ram. The actual box had 450MHz/2MB Xeons. I also moved the system disks from the onboard 7890 to a 2940 on the PCI bus. Some things are noticably faster, some are noticably slower. I have timings on "make -j N world" from an earlier incarnation of the system. It used 400MHz/512MB cache Xeons in it. I did similar tests with the Athlon. The numbers are: -j Athlon Dual Xeon 1 01:12:20 02:05:15 2 00:49:14 01:16:01 4 00:44:12 01:04:47 8 00:43:37 01:01:05 16 00:43:46 01:00:40 32 00:44:02 01:00:36 While the hardware is essentially identical except as noted, the Dual Xeons are running on FreeBSD 4-STABLE as of mid February, and the Athlon on 4-STABLE as of October, with file systems dumped and restored to take advantage of the dirpref code. Make of it them what you will. The real kicker is that the Athlon board - complete with CPU and 256Meg of 266MHz memory - has about the same street price as the two Xeons it replaced, or an empty dual Xeon motherboard. Dual CPU motherboards seem to have the same price no matter what CPU they support, so there's a significant bang/buck advantage to the Athlon cpus. I'd say that, unless you know the cache on the Xeons is going to be a win - and don't forget that cache misses are still twice as fast as cache misses on the Xeon, and roughly half the speed of cache *hits* on the Xeon - go with the Athlon. > One specific question might be, at what bus speed and mhz speed do the > advantages of a "good" processor like a xeon start to not matter ? It depoends on what advantages you're looking for. If your code and data fit in a megabyte, a 450MHz PII/Xeon with 2MB of cache will probably outperform most Athelons on the task at hand, as pretty much everything will run at 450MHz, instead of some of it running at 266MHz and some at 1.7GHz. But that's not your application. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Q: How do you make the gods laugh? A: Tell them your plans. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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