From owner-svn-src-head@FreeBSD.ORG Tue Jul 9 05:45:16 2013 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 3279C107 for ; Tue, 9 Jul 2013 05:45:16 +0000 (UTC) (envelope-from peter@wemm.org) Received: from mail-vc0-x22f.google.com (mail-vc0-x22f.google.com [IPv6:2607:f8b0:400c:c03::22f]) by mx1.freebsd.org (Postfix) with ESMTP id E64A6191F for ; Tue, 9 Jul 2013 05:45:15 +0000 (UTC) Received: by mail-vc0-f175.google.com with SMTP id hr11so4030758vcb.34 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=GFXRclKnvPOeA0Bp8rhfwStsbQeO1apMC24LcqFryq3gTZg2apM8/GlMS4NAIfCeqX hd/ZbFt+VaZPm2AK5ZUKTKQEIlXNCJmfCLZB8Uoz0P8BQoEbH1+5ISlSBEzGV7Iu2M8C uUcfnTqw/TUju8+jyWEjkP8TK5d3JQHK+HJHbBwUzhauWYSvEfxlt5f/T+FhL7r1gvhj TUdf01JX6PTqOolhL6GUyrQryGupBtfFodqmVCCxV8RrrA3BQHa34b9BbjGB7TQHveON 988CMYNOmsb8kVF1xsGVt2miKaoSudZRsQwjyqY9/Y8wjjmz5XkMkLCguX+kCVYGnCcD y2sQ== 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: ALoCoQn5g65Fr3d3/BsjBic9g3TWCzcbjMg1jPTK1TCZxDt6xxtmKqFfnvwWCJkI5h85W8Kb4WA8 Cc: "svn-src-head@freebsd.org" , "svn-src-all@freebsd.org" , Alfred Perlstein , "src-committers@freebsd.org" , Garrett Cooper X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: SVN commit messages for the src tree for head/-current 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"