From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e39.co.us.ibm.com (e39.co.us.ibm.com [32.97.110.160]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id C922F1A00A5 for ; Mon, 5 Jan 2015 15:39:20 +1100 (AEDT) Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 4 Jan 2015 21:39:18 -0700 Received: from b03cxnp08025.gho.boulder.ibm.com (b03cxnp08025.gho.boulder.ibm.com [9.17.130.17]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id B2AA73E40044 for ; Sun, 4 Jan 2015 21:39:15 -0700 (MST) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by b03cxnp08025.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t054dUeC23396408 for ; Sun, 4 Jan 2015 21:39:30 -0700 Received: from d03av01.boulder.ibm.com (localhost [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t054dDUh017952 for ; Sun, 4 Jan 2015 21:39:15 -0700 Date: Sun, 4 Jan 2015 08:14:16 -0800 From: "Paul E. McKenney" To: Michael Ellerman Subject: Re: [PATCH v2] srcu: Isolate srcu sections using CONFIG_SRCU Message-ID: <20150104161416.GA5280@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1419918382-4758-1-git-send-email-bobby.prani@gmail.com> <1419918382-4758-2-git-send-email-bobby.prani@gmail.com> <20141230185008.GA23965@worktop.programming.kicks-ass.net> <1420364152.26772.0.camel@ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1420364152.26772.0.camel@ellerman.id.au> Cc: Peter Zijlstra , Heiko Carstens , Tiejun Chen , Paul Mackerras , Daniel Walter , Ingo Molnar , "open list:S390" , Vincent Guittot , Christian Borntraeger , Jens Freimann , Pranith Kumar , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Anton Blanchard , Scott Wood , Lai Jiangshan , Li Zhong , Nishanth Aravamudan , open list , "Srivatsa S. Bhat" , Martin Schwidefsky , "supporter:S390" , "open list:LINUX FOR POWERPC..." List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, Jan 04, 2015 at 08:35:52PM +1100, Michael Ellerman wrote: > On Tue, 2014-12-30 at 13:54 -0500, Pranith Kumar wrote: > > On Tue, Dec 30, 2014 at 1:50 PM, Peter Zijlstra wrote: > > > On Tue, Dec 30, 2014 at 12:46:22AM -0500, Pranith Kumar wrote: > > >> Isolate the SRCU functions and data structures within CONFIG_SRCU so that there > > >> is a compile time failure if srcu is used when not enabled. This was decided to > > >> be better than waiting until link time for a failure to occur. > > > > > > Why? > > > > This is part of the kernel tinification efforts. The first patch was > > posted here: https://lkml.org/lkml/2014/12/4/848. This patch enables a > > compile time failure instead of a link time failure. > > The punch line was: > > "so the savings are about ~2000 bytes." > > Which is utterly not worth the effort IMO. There have got to be more attractive > targets for tinification than this. There probably are. But if the tinification effort is to come anywhere near reaching its goals, it is going to need 2000-byte savings, especially on the small systems that are this effort's main target. That said, Peter's suggestion of falling back to the link-time diagnostic does simplify things a bit, and might be a good approach. Thanx, Paul