Date: Mon, 8 Jul 2013 22:45:15 -0700 From: Peter Wemm <peter@wemm.org> To: Devin Teske <dteske@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>, Garrett Cooper <yaneurabeya@gmail.com> Subject: Re: svn commit: r253002 - head Message-ID: <CAGE5yCotsCyCR3zDRC=VhPw76vgh34Orord9os3LmGOS41jwKA@mail.gmail.com> In-Reply-To: <13CA24D6AB415D428143D44749F57D7201FB7609@ltcfiswmsgmb21> References: <201307072039.r67KdCdR028908@svn.freebsd.org> <9D4C7540-A3B0-45E5-8219-6A455D41DF70@gmail.com> <51D9DA55.2090808@freebsd.org> <13CA24D6AB415D428143D44749F57D7201FB7609@ltcfiswmsgmb21>
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On Mon, Jul 8, 2013 at 5:12 PM, Teske, Devin <Devin.Teske@fisglobal.com> wrote: > On Jul 7, 2013, at 2:15 PM, Alfred Perlstein 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. >> > > We've run as high as -j48 ... number of logical cpu's "times-two" (it was on a box with 24 logical CPUs). There's an additional constraint. -j48 and 48 running instances of clang++ and its memory demands when compiling C++ code each starts to get non-trivial. > We did buildworld in under 9 minutes. Beyond the "times-two" rule we saw a slow-down. > > NOTE: I might also mention this was on RAID-1 SSD. On the cluster we get about 9 minutes on RELENG_9 with WITHOUT_CLANG. About 11 minutes including the kernel. Boring old disks with -j24. I'd be pleasantly surprised if you were doing HEAD in < 9 minutes given that it frequently fails to build with more than -j8 or -j10. (I've heard this might be fixed.. but I'm skeptical as I had a -j2 race last week) But we are talking about a commit giving advice for building kernels here, right? >>>> Log: >>>> Document tip on how to build all kernels quickly. I used to use -j1000 to stress test context switching with a LINT build - that was when we ran into FD_SETSIZE vs make. Kernel builds have always been highly tolerant of very large -j values because idiots like me used to use it to try and break things. -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com; KI6FJV UTF-8: So you can \342\200\231 .. for when a ' just won't do <brueffer> ZFS must be the bacon of file systems. "everything's better with ZFS"
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