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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 09/10] rcu/nocb: Reduce ->nocb_lock contention with separate ->nocb_gp_lock Date: Thu, 1 Aug 2019 16:16:34 -0700 Message-Id: <20190801231636.23115-9-paulmck@linux.ibm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190801231619.GA22610@linux.ibm.com> References: <20190801231619.GA22610@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_10:,, 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-1908010245 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The sleep/wakeup of the no-CBs grace-period kthreads is synchronized using the ->nocb_lock of the first CPU corresponding to that kthread. This commit provides a separate ->nocb_gp_lock for this purpose, thus reducing contention on ->nocb_lock. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.h | 3 ++- kernel/rcu/tree_plugin.h | 9 +++++---- 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 7062f9d9c053..2c3e9068671c 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -202,7 +202,8 @@ struct rcu_data { struct timer_list nocb_timer; /* Enforce finite deferral. */ /* The following fields are used by GP kthread, hence own cacheline. */ - bool nocb_gp_sleep ____cacheline_internodealigned_in_smp; + raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp; + bool nocb_gp_sleep; /* Is the nocb GP thread asleep? */ struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */ bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 7fbf2c4411a1..af9cbc7d4784 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1602,9 +1602,9 @@ static void wake_nocb_gp(struct rcu_data *rdp, bool force, del_timer(&rdp->nocb_timer); rcu_nocb_unlock_irqrestore(rdp, flags); smp_mb(); /* enqueue before ->nocb_gp_sleep. */ - rcu_nocb_lock_irqsave(rdp_gp, flags); + raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); WRITE_ONCE(rdp_gp->nocb_gp_sleep, false); - rcu_nocb_unlock_irqrestore(rdp_gp, flags); + raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); wake_up_process(rdp_gp->nocb_gp_kthread); } else { rcu_nocb_unlock_irqrestore(rdp, flags); @@ -1759,9 +1759,9 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait")); } if (!rcu_nocb_poll) { - rcu_nocb_lock_irqsave(my_rdp, flags); + raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags); WRITE_ONCE(my_rdp->nocb_gp_sleep, true); - rcu_nocb_unlock_irqrestore(my_rdp, flags); + raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags); } WARN_ON(signal_pending(current)); } @@ -1941,6 +1941,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) init_swait_queue_head(&rdp->nocb_cb_wq); init_swait_queue_head(&rdp->nocb_gp_wq); raw_spin_lock_init(&rdp->nocb_lock); + raw_spin_lock_init(&rdp->nocb_gp_lock); timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); } -- 2.17.1