On Mon, Jul 8, 2013 at 5:12 PM, Teske, Devin <devin.te...@fisglobal.com> wrote: > On Jul 7, 2013, at 2:15 PM, Alfred Perlstein wrote: > >> On 7/7/13 2:01 PM, Garrett Cooper wrote: >>> Why the magic number 12? >> >> Numbers higher seem to result in worse performance as reported by some >> members of my team. >> > > We've run as high as -j48 ... number of logical cpu's "times-two" (it was on > a box with 24 logical CPUs).
There's an additional constraint. -j48 and 48 running instances of clang++ and its memory demands when compiling C++ code each starts to get non-trivial. > We did buildworld in under 9 minutes. Beyond the "times-two" rule we saw a > slow-down. > > NOTE: I might also mention this was on RAID-1 SSD. On the cluster we get about 9 minutes on RELENG_9 with WITHOUT_CLANG. About 11 minutes including the kernel. Boring old disks with -j24. I'd be pleasantly surprised if you were doing HEAD in < 9 minutes given that it frequently fails to build with more than -j8 or -j10. (I've heard this might be fixed.. but I'm skeptical as I had a -j2 race last week) But we are talking about a commit giving advice for building kernels here, right? >>>> Log: >>>> Document tip on how to build all kernels quickly. I used to use -j1000 to stress test context switching with a LINT build - that was when we ran into FD_SETSIZE vs make. Kernel builds have always been highly tolerant of very large -j values because idiots like me used to use it to try and break things. -- Peter Wemm - pe...@wemm.org; pe...@freebsd.org; pe...@yahoo-inc.com; KI6FJV UTF-8: So you can \342\200\231 .. for when a ' just won't do <brueffer> ZFS must be the bacon of file systems. "everything's better with ZFS" _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
