From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753814AbeB0Ph5 (ORCPT ); Tue, 27 Feb 2018 10:37:57 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:40220 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753561AbeB0Phz (ORCPT ); Tue, 27 Feb 2018 10:37:55 -0500 Date: Tue, 27 Feb 2018 07:36:46 -0800 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, Ingo Molnar Subject: Re: [PATCH tip/core/rcu 06/10] trace: Eliminate cond_resched_rcu_qs() in favor of cond_resched() Reply-To: paulmck@linux.vnet.ibm.com References: <20171201192122.GA19301@linux.vnet.ibm.com> <1512156104-20104-6-git-send-email-paulmck@linux.vnet.ibm.com> <20180224151240.0d63a059@vmware.local.home> <20180225174927.GC2855@linux.vnet.ibm.com> <20180225181730.GA3963@linux.vnet.ibm.com> <20180225183944.GA8840@linux.vnet.ibm.com> <20180226212920.43e25d6e@vmware.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180226212920.43e25d6e@vmware.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18022715-0036-0000-0000-000002C75105 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008601; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000254; SDB=6.00995884; UDB=6.00506244; IPR=6.00775209; MB=3.00019762; MTD=3.00000008; XFM=3.00000015; UTC=2018-02-27 15:36:23 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18022715-0037-0000-0000-0000437AC651 Message-Id: <20180227153646.GD3777@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-02-27_05:,, 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-1802270196 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 26, 2018 at 09:29:20PM -0500, Steven Rostedt wrote: > On Sun, 25 Feb 2018 10:39:44 -0800 > "Paul E. McKenney" wrote: > > > > Hmmm... Grasping at straws... Could we make cond_resched() be something > > > like a tracepoint and instrument them with cond_resched_rcu_qs() if the > > > current RCU-tasks grace period ran for more that (say) a minute of its > > > ten-minute stall-warning span? > > > > On the other hand, you noted in your other email that the tracepoint > > benchmark should not be enabled on production systems. So how about > > the following (again untested) patch? The "defined(CONFIG_TASKS_RCU)" > > might need to change, especially if RCU-tasks is used in production > > kernels, but perhaps a starting point. > > RCU tasks are used in production systems if PREEMPT is enabled (it > allows for optimizations with ftrace, perf and kprobes). > > But the tracepoint is not used. Right, so I should use defined(CONFIG_TRACEPOINT_BENCHMARK) instead of defined(CONFIG_TASKS_RCU). Or am I misinterpreting the code in kernel/trace? > > ------------------------------------------------------------------------ > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index b161ef8a902e..316c29c5e506 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1589,6 +1589,12 @@ static inline int test_tsk_need_resched(struct task_struct *tsk) > > */ > > #ifndef CONFIG_PREEMPT > > extern int _cond_resched(void); > > +#elif defined(CONFIG_TASKS_RCU) > > +static inline int _cond_resched(void) > > +{ > > + rcu_note_voluntary_context_switch(current); > > + return 0; > > +} > > #else > > static inline int _cond_resched(void) { return 0; } > > #endif > > > This does work, but so does the below, without causing cond_resched() > from being something other than a nop of CONFIG_PREEMPT. True, but based on the cond_resched_rcu_qs() experience, I bet that trace_benchmark.c won't be the only place needing help. Thanx, Paul > -- Steve > > diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c > index 22fee766081b..82d83bb4874b 100644 > --- a/kernel/trace/trace_benchmark.c > +++ b/kernel/trace/trace_benchmark.c > @@ -166,6 +166,7 @@ static int benchmark_event_kthread(void *arg) > * block synchronize_rcu_tasks() indefinitely. > */ > cond_resched(); > + rcu_note_voluntary_context_switch(current); > } > > return 0; >