From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E00EC63697 for ; Fri, 13 Nov 2020 12:15:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B7902085B for ; Fri, 13 Nov 2020 12:15:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="wztBpdYn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726768AbgKMMOD (ORCPT ); Fri, 13 Nov 2020 07:14:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:47598 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726524AbgKMMN6 (ORCPT ); Fri, 13 Nov 2020 07:13:58 -0500 Received: from localhost.localdomain (unknown [176.167.84.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D2E072224F; Fri, 13 Nov 2020 12:13:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605269636; bh=6Y5uordAfeofVR5BOJzczFTEpbIiasTgaOMNPIaZoYg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wztBpdYn2wbBqCDKFgsGKTR6MFGuRwzazsBUKy+9WEfhhyFXoSYVePTAVPE97w73q yM05jXsbOutw9wukhXIe17ZeFt9w91/YqEBCCvW2swlwPywCgi3LBj2Ai07aYAc/7S R15I9dK0XLNefbddtT0ib/QkELAKrbAX9GA6FRJQ= From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Steven Rostedt , Thomas Gleixner , Mathieu Desnoyers , Boqun Feng , Lai Jiangshan , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , rcu@vger.kernel.org Subject: [PATCH 04/19] rcu/nocb: De-offloading CB kthread Date: Fri, 13 Nov 2020 13:13:19 +0100 Message-Id: <20201113121334.166723-5-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201113121334.166723-1-frederic@kernel.org> References: <20201113121334.166723-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In order to de-offload the callbacks processing of an rdp, we must clear SEGCBLIST_OFFLOAD and notify the CB kthread so that it clears its own bit flag and goes to sleep to stop handling callbacks. The GP kthread will also be notified the same way. Whoever acknowledges and clears its own bit last must notify the de-offloading worker so that it can resume the de-offloading while being sure that callbacks won't be handled remotely anymore. Inspired-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay Cc: Thomas Gleixner Cc: Boqun Feng --- include/linux/rcupdate.h | 2 + kernel/rcu/rcu_segcblist.c | 10 ++- kernel/rcu/rcu_segcblist.h | 2 +- kernel/rcu/tree.h | 1 + kernel/rcu/tree_plugin.h | 131 +++++++++++++++++++++++++++++++------ 5 files changed, 123 insertions(+), 23 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index de0826411311..40266eb418b6 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -104,8 +104,10 @@ static inline void rcu_user_exit(void) { } #ifdef CONFIG_RCU_NOCB_CPU void rcu_init_nohz(void); +int rcu_nocb_cpu_deoffload(int cpu); #else /* #ifdef CONFIG_RCU_NOCB_CPU */ static inline void rcu_init_nohz(void) { } +static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ /** diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c index d7cb9dc044ea..ccfa09cb2431 100644 --- a/kernel/rcu/rcu_segcblist.c +++ b/kernel/rcu/rcu_segcblist.c @@ -252,10 +252,14 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp) * Mark the specified rcu_segcblist structure as offloaded. This * structure must be empty. */ -void rcu_segcblist_offload(struct rcu_segcblist *rsclp) +void rcu_segcblist_offload(struct rcu_segcblist *rsclp, bool offload) { - rcu_segcblist_clear_flags(rsclp, SEGCBLIST_SOFTIRQ_ONLY); - rcu_segcblist_set_flags(rsclp, SEGCBLIST_OFFLOADED); + if (offload) { + rcu_segcblist_clear_flags(rsclp, SEGCBLIST_SOFTIRQ_ONLY); + rcu_segcblist_set_flags(rsclp, SEGCBLIST_OFFLOADED); + } else { + rcu_segcblist_clear_flags(rsclp, SEGCBLIST_OFFLOADED); + } } /* diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h index 70e108c0e7c9..f42f7a13faa0 100644 --- a/kernel/rcu/rcu_segcblist.h +++ b/kernel/rcu/rcu_segcblist.h @@ -106,7 +106,7 @@ void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp); void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v); void rcu_segcblist_init(struct rcu_segcblist *rsclp); void rcu_segcblist_disable(struct rcu_segcblist *rsclp); -void rcu_segcblist_offload(struct rcu_segcblist *rsclp); +void rcu_segcblist_offload(struct rcu_segcblist *rsclp, bool offload); bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp); bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp); struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp); diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 7708ed161f4a..e0deb4829847 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -201,6 +201,7 @@ struct rcu_data { /* 5) Callback offloading. */ #ifdef CONFIG_RCU_NOCB_CPU struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */ + struct swait_queue_head nocb_state_wq; /* For offloading state changes */ struct task_struct *nocb_gp_kthread; raw_spinlock_t nocb_lock; /* Guard following pair of fields. */ atomic_t nocb_lock_contended; /* Contention experienced. */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 7e291ce0a1d6..08eb035da9e7 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2081,16 +2081,29 @@ static int rcu_nocb_gp_kthread(void *arg) return 0; } +static inline bool nocb_cb_can_run(struct rcu_data *rdp) +{ + u8 flags = SEGCBLIST_OFFLOADED | SEGCBLIST_KTHREAD_CB; + return rcu_segcblist_test_flags(&rdp->cblist, flags); +} + +static inline bool nocb_cb_wait_cond(struct rcu_data *rdp) +{ + return nocb_cb_can_run(rdp) && !READ_ONCE(rdp->nocb_cb_sleep); +} + /* * Invoke any ready callbacks from the corresponding no-CBs CPU, * then, if there are no more, wait for more to appear. */ static void nocb_cb_wait(struct rcu_data *rdp) { - unsigned long cur_gp_seq; - unsigned long flags; + struct rcu_segcblist *cblist = &rdp->cblist; + struct rcu_node *rnp = rdp->mynode; + bool needwake_state = false; bool needwake_gp = false; - struct rcu_node *rnp = rdp->mynode; + unsigned long cur_gp_seq; + unsigned long flags; local_irq_save(flags); rcu_momentary_dyntick_idle(); @@ -2100,32 +2113,50 @@ static void nocb_cb_wait(struct rcu_data *rdp) local_bh_enable(); lockdep_assert_irqs_enabled(); rcu_nocb_lock_irqsave(rdp, flags); - if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && + if (rcu_segcblist_nextgp(cblist, &cur_gp_seq) && rcu_seq_done(&rnp->gp_seq, cur_gp_seq) && raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */ needwake_gp = rcu_advance_cbs(rdp->mynode, rdp); raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ } - if (rcu_segcblist_ready_cbs(&rdp->cblist)) { - rcu_nocb_unlock_irqrestore(rdp, flags); - if (needwake_gp) - rcu_gp_kthread_wake(); - return; - } - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep")); WRITE_ONCE(rdp->nocb_cb_sleep, true); + + if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) { + if (rcu_segcblist_ready_cbs(cblist)) + WRITE_ONCE(rdp->nocb_cb_sleep, false); + } else { + /* + * De-offloading. Clear our flag and notify the de-offload worker. + * We won't touch the callbacks and keep sleeping until we ever + * get re-offloaded. + */ + WARN_ON_ONCE(!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)); + rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_CB); + if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) + needwake_state = true; + } + + if (rdp->nocb_cb_sleep) + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep")); + rcu_nocb_unlock_irqrestore(rdp, flags); if (needwake_gp) rcu_gp_kthread_wake(); - swait_event_interruptible_exclusive(rdp->nocb_cb_wq, - !READ_ONCE(rdp->nocb_cb_sleep)); - if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */ + + if (needwake_state) + swake_up_one(&rdp->nocb_state_wq); + + do { + swait_event_interruptible_exclusive(rdp->nocb_cb_wq, + nocb_cb_wait_cond(rdp)); + /* ^^^ Ensure CB invocation follows _sleep test. */ - return; - } - WARN_ON(signal_pending(current)); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); + if (smp_load_acquire(&rdp->nocb_cb_sleep)) { + WARN_ON(signal_pending(current)); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); + } + } while (!nocb_cb_can_run(rdp)); } /* @@ -2187,6 +2218,66 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) do_nocb_deferred_wakeup_common(rdp); } +static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp) +{ + struct rcu_segcblist *cblist = &rdp->cblist; + bool wake_cb = false; + unsigned long flags; + + printk("De-offloading %d\n", rdp->cpu); + + rcu_nocb_lock_irqsave(rdp, flags); + rcu_segcblist_offload(cblist, false); + + if (rdp->nocb_cb_sleep) { + rdp->nocb_cb_sleep = false; + wake_cb = true; + } + rcu_nocb_unlock_irqrestore(rdp, flags); + + if (wake_cb) + swake_up_one(&rdp->nocb_cb_wq); + + swait_event_exclusive(rdp->nocb_state_wq, + !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)); + + return 0; +} + +static long rcu_nocb_rdp_deoffload(void *arg) +{ + struct rcu_data *rdp = arg; + + WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id()); + return __rcu_nocb_rdp_deoffload(rdp); +} + +int rcu_nocb_cpu_deoffload(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + int ret = 0; + + if (rdp == rdp->nocb_gp_rdp) { + pr_info("Can't deoffload an rdp GP leader (yet)\n"); + return -EINVAL; + } + mutex_lock(&rcu_state.barrier_mutex); + cpus_read_lock(); + if (rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (cpu_online(cpu)) { + ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp); + } else { + ret = __rcu_nocb_rdp_deoffload(rdp); + } + if (!ret) + cpumask_clear_cpu(cpu, rcu_nocb_mask); + } + cpus_read_unlock(); + mutex_unlock(&rcu_state.barrier_mutex); + + return ret; +} + void __init rcu_init_nohz(void) { int cpu; @@ -2229,7 +2320,8 @@ void __init rcu_init_nohz(void) rdp = per_cpu_ptr(&rcu_data, cpu); if (rcu_segcblist_empty(&rdp->cblist)) rcu_segcblist_init(&rdp->cblist); - rcu_segcblist_offload(&rdp->cblist); + rcu_segcblist_offload(&rdp->cblist, true); + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB); } rcu_organize_nocb_kthreads(); } @@ -2239,6 +2331,7 @@ 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); + init_swait_queue_head(&rdp->nocb_state_wq); raw_spin_lock_init(&rdp->nocb_lock); raw_spin_lock_init(&rdp->nocb_bypass_lock); raw_spin_lock_init(&rdp->nocb_gp_lock); -- 2.25.1