From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754905AbeDWMiz (ORCPT ); Mon, 23 Apr 2018 08:38:55 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43996 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754786AbeDWMiw (ORCPT ); Mon, 23 Apr 2018 08:38:52 -0400 Date: Mon, 23 Apr 2018 05:40:00 -0700 From: "Paul E. McKenney" To: Peter Zijlstra 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, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com Subject: Re: [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond_resched() help Tasks RCU Reply-To: paulmck@linux.vnet.ibm.com References: <20180423023150.GA21533@linux.vnet.ibm.com> <1524450747-22778-1-git-send-email-paulmck@linux.vnet.ibm.com> <20180423085127.GR4064@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180423085127.GR4064@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18042312-0048-0000-0000-00000261B03E X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008905; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000257; SDB=6.01022090; UDB=6.00521656; IPR=6.00801325; MB=3.00020724; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-23 12:38:50 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042312-0049-0000-0000-000044E090D7 Message-Id: <20180423124000.GL26088@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-23_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-1804230131 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 23, 2018 at 10:51:27AM +0200, Peter Zijlstra wrote: > On Sun, Apr 22, 2018 at 07:32:06PM -0700, Paul E. McKenney wrote: > > In CONFIG_PREEMPT=y kernels, cond_resched() is a complete no-op, and > > thus cannot help advance Tasks-RCU grace periods. However, such grace > > periods are only an issue in non-production benchmarking runs of the > > Linux kernel. This commit therefore makes cond_resched() invoke > > rcu_note_voluntary_context_switch() for kernels implementing Tasks RCU > > even in CONFIG_PREEMPT=y kernels. > > I'm confused.. why is having this conditional on TRACEPOINT_BENCHMARK a > sane idea? Because the TRACEPOINT_BENCHMARK tests are insane, so a similar level of insanity is required to make things work. Plus having this be unconditional would not be good for performance, as 0day has been telling me frequently over the past couple of years. All that aside, I am very open to ideas. What would you suggest? Thanx, Paul > > Reported-by: Steven Rostedt > > Signed-off-by: Paul E. McKenney > > --- > > include/linux/sched.h | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index b3d697f3b573..fe8f7178a22d 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1617,6 +1617,12 @@ static inline int test_tsk_need_resched(struct task_struct *tsk) > > */ > > #ifndef CONFIG_PREEMPT > > extern int _cond_resched(void); > > +#elif defined(CONFIG_TRACEPOINT_BENCHMARK) > > +static inline int _cond_resched(void) > > +{ > > + rcu_note_voluntary_context_switch(current); > > + return 0; > > +} > > #else > > static inline int _cond_resched(void) { return 0; } > > #endif > > -- > > 2.5.2 > > >