From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751498AbcGNTyY (ORCPT ); Thu, 14 Jul 2016 15:54:24 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:33459 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751160AbcGNTyU (ORCPT ); Thu, 14 Jul 2016 15:54:20 -0400 X-IBM-Helo: d01dlp02.pok.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Thu, 14 Jul 2016 12:54:34 -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> <20160714192959.GY7094@linux.vnet.ibm.com> <20160714193800.GN30154@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160714193800.GN30154@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: 16071419-0056-0000-0000-000000C98DFA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16071419-0057-0000-0000-000004E3A194 Message-Id: <20160714195434.GZ7094@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-1607140210 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 14, 2016 at 09:38:00PM +0200, Peter Zijlstra wrote: > On Thu, Jul 14, 2016 at 12:29:59PM -0700, Paul E. McKenney wrote: > > On Thu, Jul 14, 2016 at 09:20:18PM +0200, Peter Zijlstra wrote: > > > /** > > > + * 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? > > Right, so the important thing is that its not GP_IDLE, the rest doesn't > really matter. > > This forces rcu_sync_is_idle() to return false. The skewed gp_count > ensures rcu_sync_{enter,exit}() pairs no-op. Understood. But let's have at least some pity on the poor people who might one day read this code. Thanx, Paul