From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752471AbeENRUu (ORCPT ); Mon, 14 May 2018 13:20:50 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59896 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbeENRUk (ORCPT ); Mon, 14 May 2018 13:20:40 -0400 Date: Mon, 14 May 2018 10:22:05 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org, Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , byungchul.park@lge.com, kernel-team@android.com Subject: Re: [PATCH RFC 2/8] rcu: Clarify usage of cond_resched for tasks-RCU Reply-To: paulmck@linux.vnet.ibm.com References: <20180514031541.67247-1-joel@joelfernandes.org> <20180514031541.67247-3-joel@joelfernandes.org> <20180514105454.45946ad3@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180514105454.45946ad3@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18051417-0048-0000-0000-0000026CD55E X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009025; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000260; SDB=6.01032259; UDB=6.00527710; IPR=6.00811391; MB=3.00021110; MTD=3.00000008; XFM=3.00000015; UTC=2018-05-14 17:20:37 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18051417-0049-0000-0000-0000451E79C8 Message-Id: <20180514172205.GZ26088@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-14_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805140174 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 14, 2018 at 10:54:54AM -0400, Steven Rostedt wrote: > On Sun, 13 May 2018 20:15:35 -0700 > "Joel Fernandes (Google)" wrote: > > > Recently we had a discussion about cond_resched unconditionally > > recording a voluntary context switch [1]. > > > > Lets add a comment clarifying that how this API is to be used. > > > > [1] https://lkml.kernel.org/r/1526027434-21237-1-git-send-email-byungchul.park@lge.com > > > > Signed-off-by: Joel Fernandes (Google) > > --- > > include/linux/rcupdate.h | 11 ++++++++--- > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 743226176350..a9881007ece6 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -159,8 +159,12 @@ static inline void rcu_init_nohz(void) { } > > } while (0) > > > > /* > > - * Note a voluntary context switch for RCU-tasks benefit. This is a > > - * macro rather than an inline function to avoid #include hell. > > + * Note an attempt to perform a voluntary context switch for RCU-tasks benefit. > > + * > > + * This is called even in situations where a context switch didn't really > > + * happen even though it was requested. The caller uses it to indicate > > + * traversal of an RCU-tasks quiescent state. This is a macro rather than an > > + * inline function to avoid #include hell. > > I don't know. I just don't like the wording. It sounds too much like > it was written by someone that was confused for it being called when a > context switch didn't occur ;-) > > What about something more like: > > /* > * This is called to denote a RCU-task quiescent state. It is placed at > * voluntary preemption points, as RCU-task critical sections may not > * perform voluntary preemption or scheduling calls. It does not matter > * if the task is scheduled out or not, just that a voluntary preemption > * may be done. > */ s/RCU-task/RCU-tasks/ and I am good with this. Thanx, Paul > > */ > > #ifdef CONFIG_TASKS_RCU > > #define rcu_note_voluntary_context_switch_lite(t) \ > > @@ -187,7 +191,8 @@ static inline void exit_tasks_rcu_finish(void) { } > > #endif /* #else #ifdef CONFIG_TASKS_RCU */ > > > > /** > > - * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU > > + * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU. > > + * The quiescent state report is made even if cond_resched() did nothing. > > Same thing here. > > * The quiescent state report does not depend on cond_resched() scheduling. > > -- Steve > > > > * > > * This macro resembles cond_resched(), except that it is defined to > > * report potential quiescent states to RCU-tasks even if the cond_resched() >