On Sun, Jul 7, 2013 at 7:25 PM, Garrett Cooper <yaneurab...@gmail.com> wrote: > On Jul 7, 2013, at 2:15 PM, Alfred Perlstein <alf...@freebsd.org> 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. > > The suggestion is good in spirit, but this doesn't justify the reasoning for > this recommendation for all cases. > > Please revert this change and add a doc page or notes to the dev handbook > discussing what the empirical process and results were for determining this > value so people can come up with their own values that work best with their > hardware and software config. This recommendation is prone to bitrot like > some of the recommendations in tuning(7). > > Misinformation is sometimes more harmful than no information.
I spoke with Alfred over the phone and did some more careful thought about this and I'm rescinding this request. Alfred did a good job at documenting how JFLAG works (it was previously undocumented). My concern over -j12 was performance related, and after giving things more careful thought it actually makes sense why -j12 was chosen because Westmere and newer processors have issues with NUMA and cache locality between multiple processor packages as we've seen non-empirically and empirically at Isilon with FreeBSD 7 and 10 (it's a known issue that jeffr@ and jhb@ are aware of). I'll come up with a concise patch that does what Alfred was trying to achieve and have Alfred review it. Thanks (and thank you Alfred for the contribution!!!)! -Garrett _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
