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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 06/18] rcu/nocb: Remove deferred wakeup checks for extended quiescent states Date: Thu, 1 Aug 2019 16:07:58 -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: 19080123-0060-0000-0000-000003677264 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011535; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01240744; 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: 19080123-0061-0000-0000-00004A6288AB Message-Id: <20190801230810.21570-6-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=908 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 The idea behind the checks for extended quiescent states at the end of __call_rcu_nocb() is to handle cases where call_rcu() is invoked directly from within an extended quiescent state, for example, from the idle loop. However, this will result in a timer-mediated deferred wakeup, which will cause the needed wakeup to happen within a jiffy or thereabouts. There should be no forward-progress concerns, and if there are, the proper response is to exit the extended quiescent state while executing the endless blast of call_rcu() invocations, for example, using RCU_NONIDLE(). Given the more realistic case of an isolated call_rcu() invocation, there should be no problem. This commit therefore removes the checks for invoking call_rcu() within an extended quiescent state for on no-CBs CPUs. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 10 ---------- 1 file changed, 10 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index fc6133eed50a..9936a66b80bb 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1709,16 +1709,6 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, -atomic_long_read(&rdp->nocb_q_count_lazy), -rcu_get_n_cbs_nocb_cpu(rdp)); - /* - * If called from an extended quiescent state with interrupts - * disabled, invoke the RCU core in order to allow the idle-entry - * deferred-wakeup check to function. - */ - if (irqs_disabled_flags(flags) && - !rcu_is_watching() && - cpu_online(smp_processor_id())) - invoke_rcu_core(); - return true; } -- 2.17.1