From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936249AbcKNSa7 (ORCPT ); Mon, 14 Nov 2016 13:30:59 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:41565 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935606AbcKNSab (ORCPT ); Mon, 14 Nov 2016 13:30:31 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: 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, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 1/5] rcu: Abstract the dynticks momentary-idle operation Date: Mon, 14 Nov 2016 10:30:17 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20161114183000.GA27133@linux.vnet.ibm.com> References: <20161114183000.GA27133@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16111418-0012-0000-0000-000011241C2A X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006077; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00780633; UDB=6.00376455; IPR=6.00558134; BA=6.00004878; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013322; XFM=3.00000011; UTC=2016-11-14 18:30:28 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16111418-0013-0000-0000-0000472AAD8D Message-Id: <1479148221-27831-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-14_11:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1611140367 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit is the first step towards full abstraction of all accesses to the ->dynticks counter, implementing the previously open-coded atomic add of two in a new rcu_dynticks_momentary_idle() function. This abstraction will ease changes to the ->dynticks counter operation. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 96c52e43f7ca..73b2b1da912d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -278,6 +278,19 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ }; +/* + * Do a double-increment of the ->dynticks counter to emulate a + * momentary idle-CPU quiescent state. + */ +static void rcu_dynticks_momentary_idle(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + int special = atomic_add_return(2, &rdtp->dynticks); + + /* It is illegal to call this from idle state. */ + WARN_ON_ONCE(!(special & 0x1)); +} + DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr); EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr); @@ -297,7 +310,6 @@ EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr); static void rcu_momentary_dyntick_idle(void) { struct rcu_data *rdp; - struct rcu_dynticks *rdtp; int resched_mask; struct rcu_state *rsp; @@ -324,10 +336,7 @@ static void rcu_momentary_dyntick_idle(void) * quiescent state, with no need for this CPU to do anything * further. */ - rdtp = this_cpu_ptr(&rcu_dynticks); - smp_mb__before_atomic(); /* Earlier stuff before QS. */ - atomic_add(2, &rdtp->dynticks); /* QS. */ - smp_mb__after_atomic(); /* Later stuff after QS. */ + rcu_dynticks_momentary_idle(); break; } } -- 2.5.2