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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, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 18/22] rcu: Remove CPU-hotplug failsafe from force-quiescent-state code path Date: Tue, 26 Jun 2018 10:10:44 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180626002052.GA24146@linux.vnet.ibm.com> References: <20180626002052.GA24146@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18062617-0072-0000-0000-00000374C873 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009259; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01052668; UDB=6.00539668; IPR=6.00830593; MB=3.00021864; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-26 17:08:51 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062617-0073-0000-0000-0000487E75F5 Message-Id: <20180626171048.2181-18-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-26_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=957 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1806260192 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that quiescent states for newly offlined CPUs are reported either when that CPU goes offline or at the end of grace-period initialization, the CPU-hotplug failsafe in the force-quiescent-state code path is no longer needed. This commit therefore removes this failsafe. Signed-off-by: Paul E. McKenney --- include/trace/events/rcu.h | 10 +++++----- kernel/rcu/tree.c | 9 +-------- kernel/rcu/tree.h | 1 - 3 files changed, 6 insertions(+), 14 deletions(-) diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 759e7e83733d..a8d07feff6a0 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -391,11 +391,11 @@ TRACE_EVENT(rcu_quiescent_state_report, /* * Tracepoint for quiescent states detected by force_quiescent_state(). - * These trace events include the type of RCU, the grace-period number that - * was blocked by the CPU, the CPU itself, and the type of quiescent state, - * which can be "dti" for dyntick-idle mode, "ofl" for CPU offline, "kick" - * when kicking a CPU that has been in dyntick-idle mode for too long, or - * "rqc" if the CPU got a quiescent state via its rcu_qs_ctr. + * These trace events include the type of RCU, the grace-period number + * that was blocked by the CPU, the CPU itself, and the type of quiescent + * state, which can be "dti" for dyntick-idle mode, "kick" when kicking + * a CPU that has been in dyntick-idle mode for too long, or "rqc" if the + * CPU got a quiescent state via its rcu_qs_ctr. */ TRACE_EVENT(rcu_fqs, diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8704b31b696d..c698a595b932 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1188,14 +1188,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) smp_store_release(ruqp, true); } - /* Check for the CPU being offline. */ - if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) { - trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("ofl")); - rdp->offline_fqs++; - rcu_gpnum_ovf(rnp, rdp); - return 1; - } - /* * A CPU running for an extended time within the kernel can * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode, @@ -3716,6 +3708,7 @@ void rcu_cpu_starting(unsigned int cpu) nbits = bitmap_weight(&oldmask, BITS_PER_LONG); /* Allow lockless access for expedited grace periods. */ smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */ + rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */ /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags); diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 6683da6e4ecc..795d469c6f67 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -217,7 +217,6 @@ struct rcu_data { /* 4) reasons this CPU needed to be kicked by force_quiescent_state */ unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */ - unsigned long offline_fqs; /* Kicked due to being offline. */ unsigned long cond_resched_completed; /* Grace period that needs help */ /* from cond_resched(). */ -- 2.17.1