On 2010-10-22 03:15 +0200, Andrew Reid wrote: > I recently deployed some new many-core servers at work, with > 48 cores each (4x 12 core AMD 6174s), and ran into an issue where > the stock Debian kernel is compiled with CONFIG_NR_CPUS=32, > meaning it will only use the first 32 cores that it sees.
For the record, CONFIG_NR_CPUS has been increased to 512 (the maximum supported upstream) in Squeeze. > For old Debian hands like me, this is an easy fix, I just built > a new kernel configured for more cores, and it works just fine. > > But I'm curious if anyone on the list knows the rationale for > distributing kernels with this set to 32. Is that just a > reasonable number that's never been updated? Or is there some > complication that arises after 32 cores, and should I be more > careful about tuning other parameters? Basically, 32 is chosen a bit arbitrarily. But there are some problems with high values of CONFIG_NR_CPUS: - each supported CPU adds about eight kilobytes to the kernel image, wasting memory on most machines. - On Linux 2.6.28 (maybe all kernels prior to 2.6.29), module size blows up: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=516709. Sven -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/87aam6ofol....@turtle.gmx.de
