From owner-svn-src-all@FreeBSD.ORG Tue Jul 9 05:45:16 2013 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 3C07F10A for ; Tue, 9 Jul 2013 05:45:16 +0000 (UTC) (envelope-from peter@wemm.org) Received: from mail-vb0-x230.google.com (mail-vb0-x230.google.com [IPv6:2607:f8b0:400c:c02::230]) by mx1.freebsd.org (Postfix) with ESMTP id EE0CE1921 for ; Tue, 9 Jul 2013 05:45:15 +0000 (UTC) Received: by mail-vb0-f48.google.com with SMTP id w15so4023217vbf.21 for ; Mon, 08 Jul 2013 22:45:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=wemm.org; s=google; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=gYHq3ku4q4DQYe5BqaWU1PCPRkNohmxzDi8vafFtyCI=; b=MX/kqkgv+XKVRIsAVHzAMWy90ZJ5n98SPo9KKR2PZ01IEp4npqGCkT2OKa6pcevBoN jBpbstT+VJIGW2vGoJS7DCwUD0Pzqxj+tIGIt6bEGoLLwmEISxOe2nZW1zGeab0RWl6H yGy1YaHdyIYyvv52orCbYKrbJAMvewr1CZVjw= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:x-gm-message-state; bh=gYHq3ku4q4DQYe5BqaWU1PCPRkNohmxzDi8vafFtyCI=; b=KOBaZR5GnU+75Cn/NpqdyfC/5hhe8CW8R4jfQZvHtabd6Xh124FCRBbGRUHRA82sIl cPDloO7U/FFwmOhClcQllma3PNGCxtOt210t6Qec3c7mueqJ3nKRC6htqjI2vobniooJ bkyZJ8g7lhuqH9Mbfutr4TSxRtNhX0eD4wqKQn51+5tzc1TlqdZwZu+gLLa7lGuXYzo2 qI5fGp/GA8F2yMONH4q7QGd5gpddk+FtNEEqTny1hSYw3aOFFHP8d1jvdXa8zCJSEk8x l2yZeTQk5Mex74JLe9ClV/C28OqPx8i20Wvjczznxh10B7hw5TdtYX2UV/BeXse0WakV 65DQ== MIME-Version: 1.0 X-Received: by 10.220.47.131 with SMTP id n3mr15677249vcf.7.1373348715408; Mon, 08 Jul 2013 22:45:15 -0700 (PDT) Received: by 10.221.37.198 with HTTP; Mon, 8 Jul 2013 22:45:15 -0700 (PDT) In-Reply-To: <13CA24D6AB415D428143D44749F57D7201FB7609@ltcfiswmsgmb21> References: <201307072039.r67KdCdR028908@svn.freebsd.org> <9D4C7540-A3B0-45E5-8219-6A455D41DF70@gmail.com> <51D9DA55.2090808@freebsd.org> <13CA24D6AB415D428143D44749F57D7201FB7609@ltcfiswmsgmb21> Date: Mon, 8 Jul 2013 22:45:15 -0700 Message-ID: Subject: Re: svn commit: r253002 - head From: Peter Wemm To: Devin Teske Content-Type: text/plain; charset=ISO-8859-1 X-Gm-Message-State: ALoCoQk3OBOkcSdj0Del3XWEE2VC6MU38ZA4GUHzacSnaOZpd2Kv0lyS5JTm7v60eyPcKC9b0F12 Cc: "svn-src-head@freebsd.org" , "svn-src-all@freebsd.org" , Alfred Perlstein , "src-committers@freebsd.org" , Garrett Cooper X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Jul 2013 05:45:16 -0000 On Mon, Jul 8, 2013 at 5:12 PM, Teske, Devin 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 ZFS must be the bacon of file systems. "everything's better with ZFS"