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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Fri, 2 Aug 2019 00:08:12 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x71N8A5U35062172 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 1 Aug 2019 23:08:11 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DE732B206C; Thu, 1 Aug 2019 23:08:10 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BD3F0B2067; Thu, 1 Aug 2019 23:08:10 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 1 Aug 2019 23:08:10 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 2C80A16C9A48; Thu, 1 Aug 2019 16:08:12 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org 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, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 05/18] rcu/nocb: Check for deferred nocb wakeups before nohz_full early exit Date: Thu, 1 Aug 2019 16:07:57 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190801230744.GA19115@linux.ibm.com> References: <20190801230744.GA19115@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19080123-0072-0000-0000-0000044F7336 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011535; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01240743; UDB=6.00654300; IPR=6.01022168; MB=3.00028000; MTD=3.00000008; XFM=3.00000015; UTC=2019-08-01 23:08:16 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19080123-0073-0000-0000-00004CC0745F Message-Id: <20190801230810.21570-5-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=13 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908010244 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In theory, a timer is used to defer wakeups of no-CBs grace-period kthreads when the wakeup cannot be done safely directly from the call_rcu(). In practice, the one-jiffy delay is not always consistent with timely callback invocation under heavy call_rcu() loads. Therefore, there are a number of checks for a pending deferred wakeup, including from the scheduling-clock interrupt. Unfortunately, this check follows the rcu_nohz_full_cpu() early exit, which renders it useless on such CPUs. This commit therefore moves the check for the pending deferred no-CB wakeup to precede the rcu_nohz_full_cpu() early exit. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index ea479d81da7f..f1a25d17e3a0 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2739,6 +2739,10 @@ static int rcu_pending(void) /* Check for CPU stalls, if enabled. */ check_cpu_stall(rdp); + /* Does this CPU need a deferred NOCB wakeup? */ + if (rcu_nocb_need_deferred_wakeup(rdp)) + return 1; + /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */ if (rcu_nohz_full_cpu()) return 0; @@ -2763,10 +2767,6 @@ static int rcu_pending(void) unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */ return 1; - /* Does this CPU need a deferred NOCB wakeup? */ - if (rcu_nocb_need_deferred_wakeup(rdp)) - return 1; - /* nothing to do */ return 0; } -- 2.17.1