From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751641AbcGNT3r (ORCPT ); Thu, 14 Jul 2016 15:29:47 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:51285 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751170AbcGNT3p (ORCPT ); Thu, 14 Jul 2016 15:29:45 -0400 X-IBM-Helo: d01dlp01.pok.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Thu, 14 Jul 2016 12:29:59 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Oleg Nesterov , mingo@kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org, john.stultz@linaro.org, dimitrysh@google.com, romlem@google.com, ccross@google.com, tkjos@google.com Subject: Re: [PATCH 2/2] locking/percpu-rwsem: Introduce bias knob Reply-To: paulmck@linux.vnet.ibm.com References: <20160714182545.786693675@infradead.org> <20160714183022.336211504@infradead.org> <20160714184351.GA18388@redhat.com> <20160714192018.GM30154@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160714192018.GM30154@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16071419-0040-0000-0000-000000CF8E6A X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16071419-0041-0000-0000-000004A9C253 Message-Id: <20160714192959.GY7094@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-07-14_12:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1607140205 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 14, 2016 at 09:20:18PM +0200, Peter Zijlstra wrote: > On Thu, Jul 14, 2016 at 08:43:51PM +0200, Oleg Nesterov wrote: > > > > Oh well... I personally do not think this is what we want... Can't > > we just add the stupid rcu_sync_enter() into cgroup_init() at least > > for now? Yes, this means the unnecessary .sync() at boot time, but > > it will go away after cleanups I am going to send. > > Something like so then? > > --- > --- a/include/linux/rcu_sync.h > +++ b/include/linux/rcu_sync.h > @@ -59,6 +59,7 @@ static inline bool rcu_sync_is_idle(stru > } > > extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type); > +extern void rcu_sync_sabotage(struct rcu_sync *); > extern void rcu_sync_enter(struct rcu_sync *); > extern void rcu_sync_exit(struct rcu_sync *); > extern void rcu_sync_dtor(struct rcu_sync *); > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -5609,6 +5609,8 @@ int __init cgroup_init(void) > BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files)); > BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files)); > > + rcu_sync_sabotage(&cgroup_threadgroup_rwsem.rss); With a name like that... > + > get_user_ns(init_cgroup_ns.user_ns); > > mutex_lock(&cgroup_mutex); > --- a/kernel/rcu/sync.c > +++ b/kernel/rcu/sync.c > @@ -83,6 +83,21 @@ void rcu_sync_init(struct rcu_sync *rsp, > } > > /** > + * rcu_sync_sabotage() - Sabotage a fresh rcu_sync instance > + * @rsp: Pointer to rcu_sync structure to be sabotaged > + * > + * Must be called after rcu_sync_init() and before first use. > + * > + * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}() pairs > + * turn into NO-OPs. > + */ > +void rcu_sync_sabotage(struct rcu_sync *rsp) > +{ > + rsp->gp_count++; > + rsp->gp_state = !GP_IDLE; ??? A very strange way to say GP_PENDING. A new GP_DISABLED, perhaps? Thanx, Paul > +} > + > +/** > * rcu_sync_enter() - Force readers onto slowpath > * @rsp: Pointer to rcu_sync structure to use for synchronization > * >