On 7/8/13 4:24 PM, Garrett Cooper wrote:
On Mon, Jul 8, 2013 at 2:13 PM, John Baldwin <j...@freebsd.org> wrote:
On Monday, July 08, 2013 2:23:31 am Garrett Cooper wrote:
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!!!)!
Westmere is fine, it's post-Westmere that is more troublesome.
Even the 6-core Westmeres (I'm being completely dumb here as you and
Jeff know a lot more about the NUMA issue than I do as I just caught
the tail end of the conversation at BSDCan)? I'm asking because they
(iX) are using build.ix as the primary build machine and it has 2
Westmere dies with (IIRC -- please correct me if I'm wrong
Alfred/Xin/etc) 6 cores each and are SMT enabled. It also has a
boatload of RAM and disks hooked up to an mfi(4) controller (which
could be a contributing factor in the performance degradation issue).
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.
Changing it from universe to tinderbox seems like a better idea --
I'll put a short note in my proposed patch for that.
Thanks!
-Garrett
Just to clarify, the passing of jflag in the comments was there because
it seems like most of the targets default to "-j1" which out of the box
is somewhat ludicrous these days. It was only a guide such that someone
who knows what "-j" does would be like "oh that's absurd, I know a
better value" rather than just being oblivious to it (like me) or
stupidly assume that some level of auto-tuning was done (also like me)
and wind up wondering why "make universe" is taking as long as an actual
real live universe to build.
;)
-Alfred
_______________________________________________
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"
