From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932205AbdJaKJU (ORCPT ); Tue, 31 Oct 2017 06:09:20 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:50106 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754136AbdJaJ6E (ORCPT ); Tue, 31 Oct 2017 05:58:04 -0400 X-Google-Smtp-Source: ABhQp+R/XtLip6avwN0B5qz4Mk74bc2poAecd6lTyeT+m57a4onNJeMI284sYStlg3+NU2TsN5yATA== Date: Tue, 31 Oct 2017 10:57:58 +0100 From: Ingo Molnar To: Matthias Kaehlcke Cc: Shile Zhang , Peter Zijlstra , linux-kernel@vger.kernel.org, Nick Desaulniers , Douglas Anderson , Guenter Roeck Subject: Re: [PATCH v2] sched/sysctl: Fix attributes of some extern declarations Message-ID: <20171031095758.wsgbrsdz7hzn5o2n@gmail.com> References: <20171030180816.170850-1-mka@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171030180816.170850-1-mka@chromium.org> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Matthias Kaehlcke wrote: > The definition of sysctl_sched_migration_cost, sysctl_sched_nr_migrate > and sysctl_sched_time_avg includes the attribute const_debug. This > attribute is not part of the extern declaration of these variables in > include/linux/sched/sysctl.h, as a result clang generates warnings like > this: > > kernel/sched/sched.h:1618:33: warning: section attribute is specified on > redeclared variable [-Wsection] > extern const_debug unsigned int sysctl_sched_time_avg; > ^ > ./include/linux/sched/sysctl.h:42:21: note: previous declaration is here > extern unsigned int sysctl_sched_time_avg; > > The header only declares the variables when CONFIG_SCHED_DEBUG is defined, > therefore it is not necessary to duplicate the definition of const_debug. > Instead we can use the attribute __read_mostly, which is the expansion of > const_debug when CONFIG_SCHED_DEBUG is set. > > Signed-off-by: Matthias Kaehlcke > Reviewed-by: Nick Desaulniers > --- > Changes in v2: > - removed pointless include of linux/static_key.h > - added Reviewed-by tag > > include/linux/sched/sysctl.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h > index 0f5ecd4d298e..d34c823f3d36 100644 > --- a/include/linux/sched/sysctl.h > +++ b/include/linux/sched/sysctl.h > @@ -37,9 +37,9 @@ extern unsigned int sysctl_numa_balancing_scan_period_max; > extern unsigned int sysctl_numa_balancing_scan_size; > > #ifdef CONFIG_SCHED_DEBUG > -extern unsigned int sysctl_sched_migration_cost; > -extern unsigned int sysctl_sched_nr_migrate; > -extern unsigned int sysctl_sched_time_avg; > +extern __read_mostly unsigned int sysctl_sched_migration_cost; > +extern __read_mostly unsigned int sysctl_sched_nr_migrate; > +extern __read_mostly unsigned int sysctl_sched_time_avg; So I hate this change, because it pointlessly duplicates an attribute that should only matter at the definition site. The Clang warning: > kernel/sched/sched.h:1618:33: warning: section attribute is specified on > redeclared variable [-Wsection] suggests that the -Wsection warning can be turned off. The Clang build should probably do that. Thanks, Ingo