Date: Mon, 8 Jul 2013 16:24:04 -0700 From: Garrett Cooper <yaneurabeya@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, Alfred Perlstein <alfred@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org> Subject: Re: svn commit: r253002 - head Message-ID: <CAGHfRMDBB37pF-FKRvY==SM7A9oNQzMFSaPHXsHF6wfnN4J=Xg@mail.gmail.com> In-Reply-To: <201307081713.51892.jhb@freebsd.org> References: <201307072039.r67KdCdR028908@svn.freebsd.org> <D3E9FF9F-E53A-40DE-8DFF-C4A4F05566D4@gmail.com> <CAGHfRMDmRXR1jTF_CO4T8NXOPW5Soxjrq1y_eb41mKZG2yQiiw@mail.gmail.com> <201307081713.51892.jhb@freebsd.org>
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On Mon, Jul 8, 2013 at 2:13 PM, John Baldwin <jhb@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 <yaneurabeya@gmail.com> > wrote: >> > On Jul 7, 2013, at 2:15 PM, Alfred Perlstein <alfred@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
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