svn commit: r253002 - head

John Baldwin jhb at
Mon Jul 8 21:26:19 UTC 2013

On Monday, July 08, 2013 2:23:31 am Garrett Cooper wrote:
> On Sun, Jul 7, 2013 at 7:25 PM, Garrett Cooper <yaneurabeya at> 
> > On Jul 7, 2013, at 2:15 PM, Alfred Perlstein <alfred at> 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!!!)!

Westmere is fine, it's post-Westmere that is more troublesome.

I think the comment is not super useful, but don't object enough to want
it to be removed.  I always use 'make tinderbox' instead of
'make universe' though as I want build failures to be obvious.  For the
described use case of "checking if kernels build", 'tinderbox' certainly
seems to be the more appropriate target.

John Baldwin

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