On 9 January 2013 13:55, Robert P. J. Day <[email protected]> wrote: > > just noticed this in local.conf.sample: > > # For a quad-core machine, BB_NUMBER_THREADS = "4", PARALLEL_MAKE = "-j 4" > would > # be appropriate for example. > > i thought the general rule was that parallelism should be *twice* > the number of cores. that's certainly what's suggested in the yocto > QS guide:
Some time ago I wrote a script to build the linux kernel 3 times at each -jN level from 1 to 50. Then I averaged the build time on each -jN level. I got the fastest build with -jNCPUS. Going above NCPUS just added overhead, although very little. The overhead seemed to build up quite linearly from above -jNCPUS. Because the overhead is so little, having -jNCPUS*2 may not be noticeably slower than -jNCPUS. I ran the same benchmark another machine and it showed the same trend curve. Note that NCPUS must include the hyperthread cores. Best regards, Bjørn Forsman _______________________________________________ Openembedded-core mailing list [email protected] http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/openembedded-core
