diff options
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 487 |
1 files changed, 82 insertions, 405 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 1b3dd2fc0cd6..1102765f91fd 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1,27 +1,14 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ /* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * Internal non-public definitions that provide either classic * or preemptible semantics. * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License - * along with this program; if not, you can access it online at - * http://www.gnu.org/licenses/gpl-2.0.html. - * * Copyright Red Hat, 2009 * Copyright IBM Corporation, 2009 * * Author: Ingo Molnar <mingo@elte.hu> - * Paul E. McKenney <paulmck@linux.vnet.ibm.com> + * Paul E. McKenney <paulmck@linux.ibm.com> */ #include <linux/delay.h> @@ -34,17 +21,7 @@ #include "../time/tick-internal.h" #ifdef CONFIG_RCU_BOOST - #include "../locking/rtmutex_common.h" - -/* - * Control variables for per-CPU and per-rcu_node kthreads. - */ -static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); -DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); -DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); -DEFINE_PER_CPU(char, rcu_cpu_has_work); - #else /* #ifdef CONFIG_RCU_BOOST */ /* @@ -307,8 +284,8 @@ static void rcu_qs(void) __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs")); __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); - barrier(); /* Coordinate with rcu_flavor_check_callbacks(). */ - current->rcu_read_unlock_special.b.need_qs = false; + barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */ + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false); } } @@ -666,100 +643,6 @@ static void rcu_read_unlock_special(struct task_struct *t) } /* - * Dump detailed information for all tasks blocking the current RCU - * grace period on the specified rcu_node structure. - */ -static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) -{ - unsigned long flags; - struct task_struct *t; - - raw_spin_lock_irqsave_rcu_node(rnp, flags); - if (!rcu_preempt_blocked_readers_cgp(rnp)) { - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - return; - } - t = list_entry(rnp->gp_tasks->prev, - struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - /* - * We could be printing a lot while holding a spinlock. - * Avoid triggering hard lockup. - */ - touch_nmi_watchdog(); - sched_show_task(t); - } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); -} - -/* - * Dump detailed information for all tasks blocking the current RCU - * grace period. - */ -static void rcu_print_detail_task_stall(void) -{ - struct rcu_node *rnp = rcu_get_root(); - - rcu_print_detail_task_stall_rnp(rnp); - rcu_for_each_leaf_node(rnp) - rcu_print_detail_task_stall_rnp(rnp); -} - -static void rcu_print_task_stall_begin(struct rcu_node *rnp) -{ - pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", - rnp->level, rnp->grplo, rnp->grphi); -} - -static void rcu_print_task_stall_end(void) -{ - pr_cont("\n"); -} - -/* - * Scan the current list of tasks blocked within RCU read-side critical - * sections, printing out the tid of each. - */ -static int rcu_print_task_stall(struct rcu_node *rnp) -{ - struct task_struct *t; - int ndetected = 0; - - if (!rcu_preempt_blocked_readers_cgp(rnp)) - return 0; - rcu_print_task_stall_begin(rnp); - t = list_entry(rnp->gp_tasks->prev, - struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - pr_cont(" P%d", t->pid); - ndetected++; - } - rcu_print_task_stall_end(); - return ndetected; -} - -/* - * Scan the current list of tasks blocked within RCU read-side critical - * sections, printing out the tid of each that is blocking the current - * expedited grace period. - */ -static int rcu_print_task_exp_stall(struct rcu_node *rnp) -{ - struct task_struct *t; - int ndetected = 0; - - if (!rnp->exp_tasks) - return 0; - t = list_entry(rnp->exp_tasks->prev, - struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - pr_cont(" P%d", t->pid); - ndetected++; - } - return ndetected; -} - -/* * Check that the list of blocked tasks for the newly completed grace * period is in fact empty. It is a serious bug to complete a grace * period that still has RCU readers blocked! This function must be @@ -788,13 +671,13 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) } /* - * Check for a quiescent state from the current CPU. When a task blocks, - * the task is recorded in the corresponding CPU's rcu_node structure, - * which is checked elsewhere. - * - * Caller must disable hard irqs. + * Check for a quiescent state from the current CPU, including voluntary + * context switches for Tasks RCU. When a task blocks, the task is + * recorded in the corresponding CPU's rcu_node structure, which is checked + * elsewhere, hence this function need only check for quiescent states + * related to the current CPU, not to those related to tasks. */ -static void rcu_flavor_check_callbacks(int user) +static void rcu_flavor_sched_clock_irq(int user) { struct task_struct *t = current; @@ -825,69 +708,27 @@ static void rcu_flavor_check_callbacks(int user) t->rcu_read_unlock_special.b.need_qs = true; } -/** - * synchronize_rcu - wait until a grace period has elapsed. - * - * Control will return to the caller some time after a full grace - * period has elapsed, in other words after all currently executing RCU - * read-side critical sections have completed. Note, however, that - * upon return from synchronize_rcu(), the caller might well be executing - * concurrently with new RCU read-side critical sections that began while - * synchronize_rcu() was waiting. RCU read-side critical sections are - * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. - * In addition, regions of code across which interrupts, preemption, or - * softirqs have been disabled also serve as RCU read-side critical - * sections. This includes hardware interrupt handlers, softirq handlers, - * and NMI handlers. - * - * Note that this guarantee implies further memory-ordering guarantees. - * On systems with more than one CPU, when synchronize_rcu() returns, - * each CPU is guaranteed to have executed a full memory barrier since - * the end of its last RCU read-side critical section whose beginning - * preceded the call to synchronize_rcu(). In addition, each CPU having - * an RCU read-side critical section that extends beyond the return from - * synchronize_rcu() is guaranteed to have executed a full memory barrier - * after the beginning of synchronize_rcu() and before the beginning of - * that RCU read-side critical section. Note that these guarantees include - * CPUs that are offline, idle, or executing in user mode, as well as CPUs - * that are executing in the kernel. - * - * Furthermore, if CPU A invoked synchronize_rcu(), which returned - * to its caller on CPU B, then both CPU A and CPU B are guaranteed - * to have executed a full memory barrier during the execution of - * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but - * again only if the system has more than one CPU). - */ -void synchronize_rcu(void) -{ - RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || - lock_is_held(&rcu_lock_map) || - lock_is_held(&rcu_sched_lock_map), - "Illegal synchronize_rcu() in RCU read-side critical section"); - if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) - return; - if (rcu_gp_is_expedited()) - synchronize_rcu_expedited(); - else - wait_rcu_gp(call_rcu); -} -EXPORT_SYMBOL_GPL(synchronize_rcu); - /* * Check for a task exiting while in a preemptible-RCU read-side - * critical section, clean up if so. No need to issue warnings, - * as debug_check_no_locks_held() already does this if lockdep - * is enabled. + * critical section, clean up if so. No need to issue warnings, as + * debug_check_no_locks_held() already does this if lockdep is enabled. + * Besides, if this function does anything other than just immediately + * return, there was a bug of some sort. Spewing warnings from this + * function is like as not to simply obscure important prior warnings. */ void exit_rcu(void) { struct task_struct *t = current; - if (likely(list_empty(¤t->rcu_node_entry))) + if (unlikely(!list_empty(¤t->rcu_node_entry))) { + t->rcu_read_lock_nesting = 1; + barrier(); + WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true); + } else if (unlikely(t->rcu_read_lock_nesting)) { + t->rcu_read_lock_nesting = 1; + } else { return; - t->rcu_read_lock_nesting = 1; - barrier(); - t->rcu_read_unlock_special.b.blocked = true; + } __rcu_read_unlock(); rcu_preempt_deferred_qs(current); } @@ -1051,33 +892,6 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) static void rcu_preempt_deferred_qs(struct task_struct *t) { } /* - * Because preemptible RCU does not exist, we never have to check for - * tasks blocked within RCU read-side critical sections. - */ -static void rcu_print_detail_task_stall(void) -{ -} - -/* - * Because preemptible RCU does not exist, we never have to check for - * tasks blocked within RCU read-side critical sections. - */ -static int rcu_print_task_stall(struct rcu_node *rnp) -{ - return 0; -} - -/* - * Because preemptible RCU does not exist, we never have to check for - * tasks blocked within RCU read-side critical sections that are - * blocking the current expedited grace period. - */ -static int rcu_print_task_exp_stall(struct rcu_node *rnp) -{ - return 0; -} - -/* * Because there is no preemptible RCU, there can be no readers blocked, * so there is no need to check for blocked tasks. So check only for * bogus qsmask values. @@ -1088,14 +902,10 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) } /* - * Check to see if this CPU is in a non-context-switch quiescent state - * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). - * Also schedule RCU core processing. - * - * This function must be called from hardirq context. It is normally - * invoked from the scheduling-clock interrupt. + * Check to see if this CPU is in a non-context-switch quiescent state, + * namely user mode and idle loop. */ -static void rcu_flavor_check_callbacks(int user) +static void rcu_flavor_sched_clock_irq(int user) { if (user || rcu_is_cpu_rrupt_from_idle()) { @@ -1115,22 +925,6 @@ static void rcu_flavor_check_callbacks(int user) } } -/* PREEMPT=n implementation of synchronize_rcu(). */ -void synchronize_rcu(void) -{ - RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || - lock_is_held(&rcu_lock_map) || - lock_is_held(&rcu_sched_lock_map), - "Illegal synchronize_rcu() in RCU read-side critical section"); - if (rcu_blocking_is_gp()) - return; - if (rcu_gp_is_expedited()) - synchronize_rcu_expedited(); - else - wait_rcu_gp(call_rcu); -} -EXPORT_SYMBOL_GPL(synchronize_rcu); - /* * Because preemptible RCU does not exist, tasks cannot possibly exit * while in preemptible RCU read-side critical sections. @@ -1276,8 +1070,6 @@ static int rcu_boost_kthread(void *arg) static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { - struct task_struct *t; - raw_lockdep_assert_held_rcu_node(rnp); if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); @@ -1291,9 +1083,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) if (rnp->exp_tasks == NULL) rnp->boost_tasks = rnp->gp_tasks; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - t = rnp->boost_kthread_task; - if (t) - rcu_wake_cond(t, rnp->boost_kthread_status); + rcu_wake_cond(rnp->boost_kthread_task, + rnp->boost_kthread_status); } else { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } @@ -1307,11 +1098,11 @@ static void invoke_rcu_callbacks_kthread(void) unsigned long flags; local_irq_save(flags); - __this_cpu_write(rcu_cpu_has_work, 1); - if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && - current != __this_cpu_read(rcu_cpu_kthread_task)) { - rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), - __this_cpu_read(rcu_cpu_kthread_status)); + __this_cpu_write(rcu_data.rcu_cpu_has_work, 1); + if (__this_cpu_read(rcu_data.rcu_cpu_kthread_task) != NULL && + current != __this_cpu_read(rcu_data.rcu_cpu_kthread_task)) { + rcu_wake_cond(__this_cpu_read(rcu_data.rcu_cpu_kthread_task), + __this_cpu_read(rcu_data.rcu_cpu_kthread_status)); } local_irq_restore(flags); } @@ -1322,7 +1113,7 @@ static void invoke_rcu_callbacks_kthread(void) */ static bool rcu_is_callbacks_kthread(void) { - return __this_cpu_read(rcu_cpu_kthread_task) == current; + return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current; } #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) @@ -1369,11 +1160,6 @@ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp) return 0; } -static void rcu_kthread_do_work(void) -{ - rcu_do_batch(this_cpu_ptr(&rcu_data)); -} - static void rcu_cpu_kthread_setup(unsigned int cpu) { struct sched_param sp; @@ -1384,12 +1170,12 @@ static void rcu_cpu_kthread_setup(unsigned int cpu) static void rcu_cpu_kthread_park(unsigned int cpu) { - per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; + per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; } static int rcu_cpu_kthread_should_run(unsigned int cpu) { - return __this_cpu_read(rcu_cpu_has_work); + return __this_cpu_read(rcu_data.rcu_cpu_has_work); } /* @@ -1399,21 +1185,20 @@ static int rcu_cpu_kthread_should_run(unsigned int cpu) */ static void rcu_cpu_kthread(unsigned int cpu) { - unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); - char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); + unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); + char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); int spincnt; for (spincnt = 0; spincnt < 10; spincnt++) { trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); local_bh_disable(); *statusp = RCU_KTHREAD_RUNNING; - this_cpu_inc(rcu_cpu_kthread_loops); local_irq_disable(); work = *workp; *workp = 0; local_irq_enable(); if (work) - rcu_kthread_do_work(); + rcu_do_batch(this_cpu_ptr(&rcu_data)); local_bh_enable(); if (*workp == 0) { trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); @@ -1459,7 +1244,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) } static struct smp_hotplug_thread rcu_cpu_thread_spec = { - .store = &rcu_cpu_kthread_task, + .store = &rcu_data.rcu_cpu_kthread_task, .thread_should_run = rcu_cpu_kthread_should_run, .thread_fn = rcu_cpu_kthread, .thread_comm = "rcuc/%u", @@ -1476,7 +1261,7 @@ static void __init rcu_spawn_boost_kthreads(void) int cpu; for_each_possible_cpu(cpu) - per_cpu(rcu_cpu_has_work, cpu) = 0; + per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__)) return; rcu_for_each_leaf_node(rnp) @@ -1543,7 +1328,7 @@ static void rcu_prepare_kthreads(int cpu) int rcu_needs_cpu(u64 basemono, u64 *nextevt) { *nextevt = KTIME_MAX; - return rcu_cpu_has_callbacks(NULL); + return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist); } /* @@ -1562,14 +1347,6 @@ static void rcu_prepare_for_idle(void) { } -/* - * Don't bother keeping a running count of the number of RCU callbacks - * posted because CONFIG_RCU_FAST_NO_HZ=n. - */ -static void rcu_idle_count_callbacks_posted(void) -{ -} - #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ /* @@ -1652,11 +1429,8 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) lockdep_assert_irqs_disabled(); - /* Snapshot to detect later posting of non-lazy callback. */ - rdp->nonlazy_posted_snap = rdp->nonlazy_posted; - /* If no callbacks, RCU doesn't need the CPU. */ - if (!rcu_cpu_has_callbacks(&rdp->all_lazy)) { + if (rcu_segcblist_empty(&rdp->cblist)) { *nextevt = KTIME_MAX; return 0; } @@ -1670,11 +1444,12 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) rdp->last_accelerate = jiffies; /* Request timer delay depending on laziness, and round. */ - if (!rdp->all_lazy) { + rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist); + if (rdp->all_lazy) { + dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; + } else { dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies; - } else { - dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; } *nextevt = basemono + dj * TICK_NSEC; return 0; @@ -1704,7 +1479,7 @@ static void rcu_prepare_for_idle(void) /* Handle nohz enablement switches conservatively. */ tne = READ_ONCE(tick_nohz_active); if (tne != rdp->tick_nohz_enabled_snap) { - if (rcu_cpu_has_callbacks(NULL)) + if (!rcu_segcblist_empty(&rdp->cblist)) invoke_rcu_core(); /* force nohz to see update. */ rdp->tick_nohz_enabled_snap = tne; return; @@ -1717,10 +1492,8 @@ static void rcu_prepare_for_idle(void) * callbacks, invoke RCU core for the side-effect of recalculating * idle duration on re-entry to idle. */ - if (rdp->all_lazy && - rdp->nonlazy_posted != rdp->nonlazy_posted_snap) { + if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) { rdp->all_lazy = false; - rdp->nonlazy_posted_snap = rdp->nonlazy_posted; invoke_rcu_core(); return; } @@ -1756,142 +1529,49 @@ static void rcu_cleanup_after_idle(void) invoke_rcu_core(); } -/* - * Keep a running count of the number of non-lazy callbacks posted - * on this CPU. This running counter (which is never decremented) allows - * rcu_prepare_for_idle() to detect when something out of the idle loop - * posts a callback, even if an equal number of callbacks are invoked. - * Of course, callbacks should only be posted from within a trace event - * designed to be called from idle or from within RCU_NONIDLE(). - */ -static void rcu_idle_count_callbacks_posted(void) -{ - __this_cpu_add(rcu_data.nonlazy_posted, 1); -} - #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ -#ifdef CONFIG_RCU_FAST_NO_HZ - -static void print_cpu_stall_fast_no_hz(char *cp, int cpu) -{ - struct rcu_data *rdp = &per_cpu(rcu_data, cpu); - unsigned long nlpd = rdp->nonlazy_posted - rdp->nonlazy_posted_snap; - - sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", - rdp->last_accelerate & 0xffff, jiffies & 0xffff, - ulong2long(nlpd), - rdp->all_lazy ? 'L' : '.', - rdp->tick_nohz_enabled_snap ? '.' : 'D'); -} - -#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ - -static void print_cpu_stall_fast_no_hz(char *cp, int cpu) -{ - *cp = '\0'; -} - -#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ - -/* Initiate the stall-info list. */ -static void print_cpu_stall_info_begin(void) -{ - pr_cont("\n"); -} - -/* - * Print out diagnostic information for the specified stalled CPU. - * - * If the specified CPU is aware of the current RCU grace period, then - * print the number of scheduling clock interrupts the CPU has taken - * during the time that it has been aware. Otherwise, print the number - * of RCU grace periods that this CPU is ignorant of, for example, "1" - * if the CPU was aware of the previous grace period. - * - * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. - */ -static void print_cpu_stall_info(int cpu) -{ - unsigned long delta; - char fast_no_hz[72]; - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - char *ticks_title; - unsigned long ticks_value; - - /* - * We could be printing a lot while holding a spinlock. Avoid - * triggering hard lockup. - */ - touch_nmi_watchdog(); - - ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq); - if (ticks_value) { - ticks_title = "GPs behind"; - } else { - ticks_title = "ticks this GP"; - ticks_value = rdp->ticks_this_gp; - } - print_cpu_stall_fast_no_hz(fast_no_hz, cpu); - delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); - pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n", - cpu, - "O."[!!cpu_online(cpu)], - "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], - "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], - !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' : - rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' : - "!."[!delta], - ticks_value, ticks_title, - rcu_dynticks_snap(rdp) & 0xfff, - rdp->dynticks_nesting, rdp->dynticks_nmi_nesting, - rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), - READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, - fast_no_hz); -} - -/* Terminate the stall-info list. */ -static void print_cpu_stall_info_end(void) -{ - pr_err("\t"); -} - -/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */ -static void zero_cpu_stall_ticks(struct rcu_data *rdp) -{ - rdp->ticks_this_gp = 0; - rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); - WRITE_ONCE(rdp->last_fqs_resched, jiffies); -} - #ifdef CONFIG_RCU_NOCB_CPU /* * Offload callback processing from the boot-time-specified set of CPUs - * specified by rcu_nocb_mask. For each CPU in the set, there is a - * kthread created that pulls the callbacks from the corresponding CPU, - * waits for a grace period to elapse, and invokes the callbacks. - * The no-CBs CPUs do a wake_up() on their kthread when they insert - * a callback into any empty list, unless the rcu_nocb_poll boot parameter - * has been specified, in which case each kthread actively polls its - * CPU. (Which isn't so great for energy efficiency, but which does - * reduce RCU's overhead on that CPU.) + * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads + * created that pull the callbacks from the corresponding CPU, wait for + * a grace period to elapse, and invoke the callbacks. These kthreads + * are organized into leaders, which manage incoming callbacks, wait for + * grace periods, and awaken followers, and the followers, which only + * invoke callbacks. Each leader is its own follower. The no-CBs CPUs + * do a wake_up() on their kthread when they insert a callback into any + * empty list, unless the rcu_nocb_poll boot parameter has been specified, + * in which case each kthread actively polls its CPU. (Which isn't so great + * for energy efficiency, but which does reduce RCU's overhead on that CPU.) * * This is intended to be used in conjunction with Frederic Weisbecker's * adaptive-idle work, which would seriously reduce OS jitter on CPUs * running CPU-bound user-mode computations. * - * Offloading of callback processing could also in theory be used as - * an energy-efficiency measure because CPUs with no RCU callbacks - * queued are more aggressive about entering dyntick-idle mode. + * Offloading of callbacks can also be used as an energy-efficiency + * measure because CPUs with no RCU callbacks queued are more aggressive + * about entering dyntick-idle mode. */ -/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ +/* + * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. + * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a + * comma-separated list of CPUs and/or CPU ranges. If an invalid list is + * given, a warning is emitted and all CPUs are offloaded. + */ static int __init rcu_nocb_setup(char *str) { alloc_bootmem_cpumask_var(&rcu_nocb_mask); - cpulist_parse(str, rcu_nocb_mask); + if (!strcasecmp(str, "all")) + cpumask_setall(rcu_nocb_mask); + else + if (cpulist_parse(str, rcu_nocb_mask)) { + pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); + cpumask_setall(rcu_nocb_mask); + } return 1; } __setup("rcu_nocbs=", rcu_nocb_setup); @@ -1987,10 +1667,7 @@ static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype, raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); } -/* - * Does the specified CPU need an RCU callback for this invocation - * of rcu_barrier()? - */ +/* Does rcu_barrier need to queue an RCU callback on the specified CPU? */ static bool rcu_nocb_cpu_needs_barrier(int cpu) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); @@ -2006,8 +1683,8 @@ static bool rcu_nocb_cpu_needs_barrier(int cpu) * callbacks would be posted. In the worst case, the first * barrier in rcu_barrier() suffices (but the caller cannot * necessarily rely on this, not a substitute for the caller - * getting the concurrency design right!). There must also be - * a barrier between the following load an posting of a callback + * getting the concurrency design right!). There must also be a + * barrier between the following load and posting of a callback * (if a callback is in fact needed). This is associated with an * atomic_inc() in the caller. */ @@ -2517,9 +2194,9 @@ static void rcu_spawn_one_nocb_kthread(int cpu) /* * If the specified CPU is a no-CBs CPU that does not already have its - * rcuo kthreads, spawn them. + * rcuo kthread, spawn it. */ -static void rcu_spawn_all_nocb_kthreads(int cpu) +static void rcu_spawn_cpu_nocb_kthread(int cpu) { if (rcu_scheduler_fully_active) rcu_spawn_one_nocb_kthread(cpu); @@ -2536,7 +2213,7 @@ static void __init rcu_spawn_nocb_kthreads(void) int cpu; for_each_online_cpu(cpu) - rcu_spawn_all_nocb_kthreads(cpu); + rcu_spawn_cpu_nocb_kthread(cpu); } /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ @@ -2670,7 +2347,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) { } -static void rcu_spawn_all_nocb_kthreads(int cpu) +static void rcu_spawn_cpu_nocb_kthread(int cpu) { } |