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@ -1543,14 +1543,7 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
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int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
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{
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*delta_jiffies = ULONG_MAX;
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return rcu_cpu_has_callbacks(cpu);
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}
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/*
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* Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
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*/
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static void rcu_prepare_for_idle_init(int cpu)
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{
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return rcu_cpu_has_callbacks(cpu, NULL);
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}
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/*
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@ -1587,16 +1580,6 @@ static void rcu_idle_count_callbacks_posted(void)
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*
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* The following three proprocessor symbols control this state machine:
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*
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* RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt
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* to satisfy RCU. Beyond this point, it is better to incur a periodic
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* scheduling-clock interrupt than to loop through the state machine
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* at full power.
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* RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
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* optional if RCU does not need anything immediately from this
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* CPU, even if this CPU still has RCU callbacks queued. The first
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* times through the state machine are mandatory: we need to give
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* the state machine a chance to communicate a quiescent state
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* to the RCU core.
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* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
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* to sleep in dyntick-idle mode with RCU callbacks pending. This
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* is sized to be roughly one RCU grace period. Those energy-efficiency
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@ -1612,15 +1595,9 @@ static void rcu_idle_count_callbacks_posted(void)
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* adjustment, they can be converted into kernel config parameters, though
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* making the state machine smarter might be a better option.
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*/
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#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */
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#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */
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#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
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#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
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static int rcu_idle_flushes = RCU_IDLE_FLUSHES;
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module_param(rcu_idle_flushes, int, 0644);
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static int rcu_idle_opt_flushes = RCU_IDLE_OPT_FLUSHES;
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module_param(rcu_idle_opt_flushes, int, 0644);
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static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
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module_param(rcu_idle_gp_delay, int, 0644);
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static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
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@ -1629,178 +1606,97 @@ module_param(rcu_idle_lazy_gp_delay, int, 0644);
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extern int tick_nohz_enabled;
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/*
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* Does the specified flavor of RCU have non-lazy callbacks pending on
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* the specified CPU? Both RCU flavor and CPU are specified by the
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* rcu_data structure.
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* Try to advance callbacks for all flavors of RCU on the current CPU.
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* Afterwards, if there are any callbacks ready for immediate invocation,
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* return true.
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*/
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static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
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static bool rcu_try_advance_all_cbs(void)
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{
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return rdp->qlen != rdp->qlen_lazy;
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}
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bool cbs_ready = false;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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struct rcu_state *rsp;
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#ifdef CONFIG_TREE_PREEMPT_RCU
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for_each_rcu_flavor(rsp) {
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rdp = this_cpu_ptr(rsp->rda);
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rnp = rdp->mynode;
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/*
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* Are there non-lazy RCU-preempt callbacks? (There cannot be if there
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* is no RCU-preempt in the kernel.)
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*/
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static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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/*
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* Don't bother checking unless a grace period has
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* completed since we last checked and there are
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* callbacks not yet ready to invoke.
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*/
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if (rdp->completed != rnp->completed &&
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rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
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rcu_process_gp_end(rsp, rdp);
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return __rcu_cpu_has_nonlazy_callbacks(rdp);
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}
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#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
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static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
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{
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return 0;
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}
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#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
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/*
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* Does any flavor of RCU have non-lazy callbacks on the specified CPU?
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*/
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static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
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{
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return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
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__rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
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rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
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if (cpu_has_callbacks_ready_to_invoke(rdp))
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cbs_ready = true;
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}
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return cbs_ready;
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}
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/*
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* Allow the CPU to enter dyntick-idle mode if either: (1) There are no
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* callbacks on this CPU, (2) this CPU has not yet attempted to enter
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* dyntick-idle mode, or (3) this CPU is in the process of attempting to
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* enter dyntick-idle mode. Otherwise, if we have recently tried and failed
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* to enter dyntick-idle mode, we refuse to try to enter it. After all,
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* it is better to incur scheduling-clock interrupts than to spin
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* continuously for the same time duration!
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* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
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* to invoke. If the CPU has callbacks, try to advance them. Tell the
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* caller to set the timeout based on whether or not there are non-lazy
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* callbacks.
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*
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* The delta_jiffies argument is used to store the time when RCU is
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* going to need the CPU again if it still has callbacks. The reason
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* for this is that rcu_prepare_for_idle() might need to post a timer,
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* but if so, it will do so after tick_nohz_stop_sched_tick() has set
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* the wakeup time for this CPU. This means that RCU's timer can be
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* delayed until the wakeup time, which defeats the purpose of posting
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* a timer.
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* The caller must have disabled interrupts.
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*/
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int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
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int rcu_needs_cpu(int cpu, unsigned long *dj)
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{
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struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
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/* Flag a new idle sojourn to the idle-entry state machine. */
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rdtp->idle_first_pass = 1;
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/* Snapshot to detect later posting of non-lazy callback. */
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rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
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/* If no callbacks, RCU doesn't need the CPU. */
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if (!rcu_cpu_has_callbacks(cpu)) {
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*delta_jiffies = ULONG_MAX;
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if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
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*dj = ULONG_MAX;
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return 0;
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}
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if (rdtp->dyntick_holdoff == jiffies) {
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/* RCU recently tried and failed, so don't try again. */
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*delta_jiffies = 1;
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/* Attempt to advance callbacks. */
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if (rcu_try_advance_all_cbs()) {
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/* Some ready to invoke, so initiate later invocation. */
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invoke_rcu_core();
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return 1;
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}
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/* Set up for the possibility that RCU will post a timer. */
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if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
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*delta_jiffies = round_up(rcu_idle_gp_delay + jiffies,
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rcu_idle_gp_delay) - jiffies;
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rdtp->last_accelerate = jiffies;
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/* Request timer delay depending on laziness, and round. */
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if (rdtp->all_lazy) {
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*dj = round_up(rcu_idle_gp_delay + jiffies,
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rcu_idle_gp_delay) - jiffies;
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} else {
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*delta_jiffies = jiffies + rcu_idle_lazy_gp_delay;
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*delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
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*dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
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}
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return 0;
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}
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/*
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* Handler for smp_call_function_single(). The only point of this
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* handler is to wake the CPU up, so the handler does only tracing.
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*/
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void rcu_idle_demigrate(void *unused)
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{
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trace_rcu_prep_idle("Demigrate");
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}
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/*
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* Timer handler used to force CPU to start pushing its remaining RCU
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* callbacks in the case where it entered dyntick-idle mode with callbacks
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* pending. The hander doesn't really need to do anything because the
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* real work is done upon re-entry to idle, or by the next scheduling-clock
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* interrupt should idle not be re-entered.
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*
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* One special case: the timer gets migrated without awakening the CPU
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* on which the timer was scheduled on. In this case, we must wake up
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* that CPU. We do so with smp_call_function_single().
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*/
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static void rcu_idle_gp_timer_func(unsigned long cpu_in)
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{
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int cpu = (int)cpu_in;
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trace_rcu_prep_idle("Timer");
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if (cpu != smp_processor_id())
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smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
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else
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WARN_ON_ONCE(1); /* Getting here can hang the system... */
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}
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/*
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* Initialize the timer used to pull CPUs out of dyntick-idle mode.
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*/
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static void rcu_prepare_for_idle_init(int cpu)
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{
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struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
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rdtp->dyntick_holdoff = jiffies - 1;
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setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
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rdtp->idle_gp_timer_expires = jiffies - 1;
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rdtp->idle_first_pass = 1;
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}
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/*
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* Clean up for exit from idle. Because we are exiting from idle, there
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* is no longer any point to ->idle_gp_timer, so cancel it. This will
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* do nothing if this timer is not active, so just cancel it unconditionally.
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*/
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static void rcu_cleanup_after_idle(int cpu)
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{
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struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
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del_timer(&rdtp->idle_gp_timer);
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trace_rcu_prep_idle("Cleanup after idle");
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rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);
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}
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/*
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* Check to see if any RCU-related work can be done by the current CPU,
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* and if so, schedule a softirq to get it done. This function is part
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* of the RCU implementation; it is -not- an exported member of the RCU API.
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*
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* The idea is for the current CPU to clear out all work required by the
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* RCU core for the current grace period, so that this CPU can be permitted
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* to enter dyntick-idle mode. In some cases, it will need to be awakened
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* at the end of the grace period by whatever CPU ends the grace period.
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* This allows CPUs to go dyntick-idle more quickly, and to reduce the
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* number of wakeups by a modest integer factor.
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*
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* Because it is not legal to invoke rcu_process_callbacks() with irqs
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* disabled, we do one pass of force_quiescent_state(), then do a
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* invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
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* later. The ->dyntick_drain field controls the sequencing.
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* Prepare a CPU for idle from an RCU perspective. The first major task
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* is to sense whether nohz mode has been enabled or disabled via sysfs.
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* The second major task is to check to see if a non-lazy callback has
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* arrived at a CPU that previously had only lazy callbacks. The third
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* major task is to accelerate (that is, assign grace-period numbers to)
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* any recently arrived callbacks.
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*
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* The caller must have disabled interrupts.
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*/
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static void rcu_prepare_for_idle(int cpu)
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{
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struct timer_list *tp;
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struct rcu_data *rdp;
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struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
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struct rcu_node *rnp;
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struct rcu_state *rsp;
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int tne;
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/* Handle nohz enablement switches conservatively. */
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tne = ACCESS_ONCE(tick_nohz_enabled);
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if (tne != rdtp->tick_nohz_enabled_snap) {
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if (rcu_cpu_has_callbacks(cpu))
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if (rcu_cpu_has_callbacks(cpu, NULL))
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invoke_rcu_core(); /* force nohz to see update. */
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rdtp->tick_nohz_enabled_snap = tne;
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return;
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@ -1808,125 +1704,56 @@ static void rcu_prepare_for_idle(int cpu)
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if (!tne)
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return;
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|
|
/* Adaptive-tick mode, where usermode execution is idle to RCU. */
|
|
|
|
|
if (!is_idle_task(current)) {
|
|
|
|
|
rdtp->dyntick_holdoff = jiffies - 1;
|
|
|
|
|
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
|
|
|
|
|
trace_rcu_prep_idle("User dyntick with callbacks");
|
|
|
|
|
rdtp->idle_gp_timer_expires =
|
|
|
|
|
round_up(jiffies + rcu_idle_gp_delay,
|
|
|
|
|
rcu_idle_gp_delay);
|
|
|
|
|
} else if (rcu_cpu_has_callbacks(cpu)) {
|
|
|
|
|
rdtp->idle_gp_timer_expires =
|
|
|
|
|
round_jiffies(jiffies + rcu_idle_lazy_gp_delay);
|
|
|
|
|
trace_rcu_prep_idle("User dyntick with lazy callbacks");
|
|
|
|
|
} else {
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
tp = &rdtp->idle_gp_timer;
|
|
|
|
|
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
|
|
|
|
|
/* If this is a no-CBs CPU, no callbacks, just return. */
|
|
|
|
|
if (is_nocb_cpu(cpu))
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* If this is an idle re-entry, for example, due to use of
|
|
|
|
|
* RCU_NONIDLE() or the new idle-loop tracing API within the idle
|
|
|
|
|
* loop, then don't take any state-machine actions, unless the
|
|
|
|
|
* momentary exit from idle queued additional non-lazy callbacks.
|
|
|
|
|
* Instead, repost the ->idle_gp_timer if this CPU has callbacks
|
|
|
|
|
* pending.
|
|
|
|
|
* If a non-lazy callback arrived at a CPU having only lazy
|
|
|
|
|
* callbacks, invoke RCU core for the side-effect of recalculating
|
|
|
|
|
* idle duration on re-entry to idle.
|
|
|
|
|
*/
|
|
|
|
|
if (!rdtp->idle_first_pass &&
|
|
|
|
|
(rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
|
|
|
|
|
if (rcu_cpu_has_callbacks(cpu)) {
|
|
|
|
|
tp = &rdtp->idle_gp_timer;
|
|
|
|
|
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
|
|
|
|
|
}
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
rdtp->idle_first_pass = 0;
|
|
|
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* If there are no callbacks on this CPU, enter dyntick-idle mode.
|
|
|
|
|
* Also reset state to avoid prejudicing later attempts.
|
|
|
|
|
*/
|
|
|
|
|
if (!rcu_cpu_has_callbacks(cpu)) {
|
|
|
|
|
rdtp->dyntick_holdoff = jiffies - 1;
|
|
|
|
|
rdtp->dyntick_drain = 0;
|
|
|
|
|
trace_rcu_prep_idle("No callbacks");
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* If in holdoff mode, just return. We will presumably have
|
|
|
|
|
* refrained from disabling the scheduling-clock tick.
|
|
|
|
|
*/
|
|
|
|
|
if (rdtp->dyntick_holdoff == jiffies) {
|
|
|
|
|
trace_rcu_prep_idle("In holdoff");
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/* Check and update the ->dyntick_drain sequencing. */
|
|
|
|
|
if (rdtp->dyntick_drain <= 0) {
|
|
|
|
|
/* First time through, initialize the counter. */
|
|
|
|
|
rdtp->dyntick_drain = rcu_idle_flushes;
|
|
|
|
|
} else if (rdtp->dyntick_drain <= rcu_idle_opt_flushes &&
|
|
|
|
|
!rcu_pending(cpu) &&
|
|
|
|
|
!local_softirq_pending()) {
|
|
|
|
|
/* Can we go dyntick-idle despite still having callbacks? */
|
|
|
|
|
rdtp->dyntick_drain = 0;
|
|
|
|
|
rdtp->dyntick_holdoff = jiffies;
|
|
|
|
|
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
|
|
|
|
|
trace_rcu_prep_idle("Dyntick with callbacks");
|
|
|
|
|
rdtp->idle_gp_timer_expires =
|
|
|
|
|
round_up(jiffies + rcu_idle_gp_delay,
|
|
|
|
|
rcu_idle_gp_delay);
|
|
|
|
|
} else {
|
|
|
|
|
rdtp->idle_gp_timer_expires =
|
|
|
|
|
round_jiffies(jiffies + rcu_idle_lazy_gp_delay);
|
|
|
|
|
trace_rcu_prep_idle("Dyntick with lazy callbacks");
|
|
|
|
|
}
|
|
|
|
|
tp = &rdtp->idle_gp_timer;
|
|
|
|
|
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
|
|
|
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
|
|
|
return; /* Nothing more to do immediately. */
|
|
|
|
|
} else if (--(rdtp->dyntick_drain) <= 0) {
|
|
|
|
|
/* We have hit the limit, so time to give up. */
|
|
|
|
|
rdtp->dyntick_holdoff = jiffies;
|
|
|
|
|
trace_rcu_prep_idle("Begin holdoff");
|
|
|
|
|
invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* Do one step of pushing the remaining RCU callbacks through
|
|
|
|
|
* the RCU core state machine.
|
|
|
|
|
*/
|
|
|
|
|
#ifdef CONFIG_TREE_PREEMPT_RCU
|
|
|
|
|
if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
|
|
|
|
|
rcu_preempt_qs(cpu);
|
|
|
|
|
force_quiescent_state(&rcu_preempt_state);
|
|
|
|
|
}
|
|
|
|
|
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
|
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
|
|
|
|
|
rcu_sched_qs(cpu);
|
|
|
|
|
force_quiescent_state(&rcu_sched_state);
|
|
|
|
|
}
|
|
|
|
|
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
|
|
|
|
|
rcu_bh_qs(cpu);
|
|
|
|
|
force_quiescent_state(&rcu_bh_state);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* If RCU callbacks are still pending, RCU still needs this CPU.
|
|
|
|
|
* So try forcing the callbacks through the grace period.
|
|
|
|
|
*/
|
|
|
|
|
if (rcu_cpu_has_callbacks(cpu)) {
|
|
|
|
|
trace_rcu_prep_idle("More callbacks");
|
|
|
|
|
if (rdtp->all_lazy &&
|
|
|
|
|
rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
|
|
|
|
|
invoke_rcu_core();
|
|
|
|
|
} else {
|
|
|
|
|
trace_rcu_prep_idle("Callbacks drained");
|
|
|
|
|
return;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* If we have not yet accelerated this jiffy, accelerate all
|
|
|
|
|
* callbacks on this CPU.
|
|
|
|
|
*/
|
|
|
|
|
if (rdtp->last_accelerate == jiffies)
|
|
|
|
|
return;
|
|
|
|
|
rdtp->last_accelerate = jiffies;
|
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
|
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
|
|
|
if (!*rdp->nxttail[RCU_DONE_TAIL])
|
|
|
|
|
continue;
|
|
|
|
|
rnp = rdp->mynode;
|
|
|
|
|
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
|
|
|
|
|
rcu_accelerate_cbs(rsp, rnp, rdp);
|
|
|
|
|
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* Clean up for exit from idle. Attempt to advance callbacks based on
|
|
|
|
|
* any grace periods that elapsed while the CPU was idle, and if any
|
|
|
|
|
* callbacks are now ready to invoke, initiate invocation.
|
|
|
|
|
*/
|
|
|
|
|
static void rcu_cleanup_after_idle(int cpu)
|
|
|
|
|
{
|
|
|
|
|
struct rcu_data *rdp;
|
|
|
|
|
struct rcu_state *rsp;
|
|
|
|
|
|
|
|
|
|
if (is_nocb_cpu(cpu))
|
|
|
|
|
return;
|
|
|
|
|
rcu_try_advance_all_cbs();
|
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
|
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
|
|
|
if (cpu_has_callbacks_ready_to_invoke(rdp))
|
|
|
|
|
invoke_rcu_core();
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@ -2034,16 +1861,13 @@ early_initcall(rcu_register_oom_notifier);
|
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
|
|
|
{
|
|
|
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
|
|
|
struct timer_list *tltp = &rdtp->idle_gp_timer;
|
|
|
|
|
char c;
|
|
|
|
|
unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
|
|
|
|
|
|
|
|
|
|
c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.';
|
|
|
|
|
if (timer_pending(tltp))
|
|
|
|
|
sprintf(cp, "drain=%d %c timer=%lu",
|
|
|
|
|
rdtp->dyntick_drain, c, tltp->expires - jiffies);
|
|
|
|
|
else
|
|
|
|
|
sprintf(cp, "drain=%d %c timer not pending",
|
|
|
|
|
rdtp->dyntick_drain, c);
|
|
|
|
|
sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
|
|
|
|
|
rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
|
|
|
|
|
ulong2long(nlpd),
|
|
|
|
|
rdtp->all_lazy ? 'L' : '.',
|
|
|
|
|
rdtp->tick_nohz_enabled_snap ? '.' : 'D');
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
|
|
Paul E. McKenney
Paul E. McKenney