From owner-svn-src-head@FreeBSD.ORG Mon Jul 8 06:23:32 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 903885A4; Mon, 8 Jul 2013 06:23:32 +0000 (UTC) (envelope-from yaneurabeya@gmail.com) Received: from mail-vb0-x22c.google.com (mail-vb0-x22c.google.com [IPv6:2607:f8b0:400c:c02::22c]) by mx1.freebsd.org (Postfix) with ESMTP id 1D0551AA9; Mon, 8 Jul 2013 06:23:32 +0000 (UTC) Received: by mail-vb0-f44.google.com with SMTP id e15so3099329vbg.31 for ; Sun, 07 Jul 2013 23:23:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=pZprHLhgQ7qljIiJE1K2R0/hlLLIgXYc59qNeR3shLc=; b=XoMlzBFLd8bfDECQIbWgmZRomBA11aE+2wzrm7gZh98A/8H/cfrtAhBZPukRRH/suM ga9HX5mPdzwxyS26tLxfGq6Oj3mL6IcSWy4fginLJwaFNUz3DtQKn19fRiVGWoxrzGMQ DT0rUc7JHEgtcIIgrijyXNXcidi9OWLOtnZ9h4kQMWpufOPcrO+k98Kev+Uscyn76/Zs yoFUeHL/mG6VYEHT/bpsAvZbJpMGgzV3L/cvkMTLUjpRjFD62sESRt9vxJQ5dXKnQWfX vHF0P1YzfZ5NeGSoTwfaZA/KHIbWPtn9k7khgdnN1DEedYGx+s6xeEPUh5zeN7W9QzoA y5Sw== MIME-Version: 1.0 X-Received: by 10.221.5.71 with SMTP id of7mr13147599vcb.39.1373264611572; Sun, 07 Jul 2013 23:23:31 -0700 (PDT) Received: by 10.220.146.145 with HTTP; Sun, 7 Jul 2013 23:23:31 -0700 (PDT) In-Reply-To: References: <201307072039.r67KdCdR028908@svn.freebsd.org> <9D4C7540-A3B0-45E5-8219-6A455D41DF70@gmail.com> <51D9DA55.2090808@freebsd.org> Date: Sun, 7 Jul 2013 23:23:31 -0700 Message-ID: Subject: Re: svn commit: r253002 - head From: Garrett Cooper To: Alfred Perlstein Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: "svn-src-head@freebsd.org" , "svn-src-all@freebsd.org" , "src-committers@freebsd.org" 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: Mon, 08 Jul 2013 06:23:32 -0000 On Sun, Jul 7, 2013 at 7:25 PM, Garrett Cooper wrot= e: > 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 m= embers 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 thi= s value so people can come up with their own values that work best with the= ir hardware and software config. This recommendation is prone to bitrot lik= e 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!!!)! -Garrett