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I have a quad socket octo-core system running FreeBSD. Currently, I need to turn off HyperThreading to get it to boot, as FreeBSD only supports 32 CPUs. There were some patches made awhile ago against a trunk version of 8.1, but even after modifying them slightly to work and compile with 8.1-RELEASE, the machine wouldn't boot.

Has there been any progress here? I can't find much good information about it, Google thinks I'm talking about 64-bit architecture and not literally 64 CPUs.

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migrated from Jan 14 '11 at 17:51

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No one will need more than 640K of RAM. :) Wow! 64 cores. Nice! – geoffc Jan 14 '11 at 18:02
Wow, as you say it really is difficult to get any information on FreeBSD using more than 64 cpus... closest I got was from 2009! – Mokubai Jan 14 '11 at 18:10
Have a look at this:… – Hunter Jan 14 '11 at 18:39

At the end of, a FreeBSD developer mentions that

AFAIR it was told somewhere that for 64bit archs it should be possible to rise [the number of logical cores] up to 64 without much troubles, except increased memory consumption. It just wasn't tested due to lack of such systems. Further increase will probably require some architectural changes.

That comment was made in April 2010. Earlier posts in the thread quote an include file which specifies the number of cores.

It might help to remember that Google will let you filter out things using syntax like -"64-bit" — though in this case, and perhaps others, the quoted result would have been filtered out. I got there by googling freebsd max cores.

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I've seen that post. However what it describes is not possible - the CPU mask is only 32 bits, that's why the maximum is currently 32. The patch I looked over did something else entirely, and wasn't exactly trivial. I've tried recompiling the kernel with simply MAXCPUS set to 64, the kernel doesn't boot unfortunately. – Brett Jan 16 '11 at 4:09

Note that MAXCPU was recently bumped to 256, but only in 11-CURRENT.

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Actually MAXCPUS was bumped I believe in 9.x. Problem has been fixed for quite some time! I don't recall what it was bumped to, but it was made to be more than an 32 bit mask. – Brett Jan 28 '15 at 0:08

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