*
* Copyright (C) IBM Corporation, 2001
*
- * Author: Dipankar Sarma <dipankar@in.ibm.com>
+ * Authors: Dipankar Sarma <dipankar@in.ibm.com>
+ * Manfred Spraul <manfred@colorfullife.com>
*
- * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
+ * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
* Papers:
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <asm/atomic.h>
-#include <asm/bitops.h>
+#include <linux/bitops.h>
#include <linux/module.h>
#include <linux/completion.h>
+#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
/* Definition for rcupdate control block. */
struct rcu_ctrlblk rcu_ctrlblk =
- { .mutex = SPIN_LOCK_UNLOCKED, .curbatch = 1,
- .maxbatch = 1, .rcu_cpu_mask = CPU_MASK_NONE };
+ { .cur = -300, .completed = -300 };
+struct rcu_ctrlblk rcu_bh_ctrlblk =
+ { .cur = -300, .completed = -300 };
+
+/* Bookkeeping of the progress of the grace period */
+struct rcu_state {
+ spinlock_t lock; /* Guard this struct and writes to rcu_ctrlblk */
+ cpumask_t cpumask; /* CPUs that need to switch in order */
+ /* for current batch to proceed. */
+};
+
+static struct rcu_state rcu_state ____cacheline_maxaligned_in_smp =
+ {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE };
+static struct rcu_state rcu_bh_state ____cacheline_maxaligned_in_smp =
+ {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE };
+
DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
+DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
/* Fake initialization required by compiler */
static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
-#define RCU_tasklet(cpu) (per_cpu(rcu_tasklet, cpu))
+static int maxbatch = 10;
+
+/**
+ * call_rcu - Queue an RCU callback for invocation after a grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual update function to be invoked after the grace period
+ *
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ */
+void fastcall call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+
+ head->func = func;
+ head->next = NULL;
+ local_irq_save(flags);
+ rdp = &__get_cpu_var(rcu_data);
+ *rdp->nxttail = head;
+ rdp->nxttail = &head->next;
+ local_irq_restore(flags);
+}
/**
- * call_rcu - Queue an RCU update request.
+ * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual update function to be invoked after the grace period
- * @arg: argument to be passed to the update function
*
- * The update function will be invoked as soon as all CPUs have performed
- * a context switch or been seen in the idle loop or in a user process.
- * The read-side of critical section that use call_rcu() for updation must
- * be protected by rcu_read_lock()/rcu_read_unlock().
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_bh() assumes
+ * that the read-side critical sections end on completion of a softirq
+ * handler. This means that read-side critical sections in process
+ * context must not be interrupted by softirqs. This interface is to be
+ * used when most of the read-side critical sections are in softirq context.
+ * RCU read-side critical sections are delimited by rcu_read_lock() and
+ * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
+ * and rcu_read_unlock_bh(), if in process context. These may be nested.
*/
-void fastcall call_rcu(struct rcu_head *head, void (*func)(void *arg), void *arg)
+void fastcall call_rcu_bh(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
{
- int cpu;
unsigned long flags;
+ struct rcu_data *rdp;
head->func = func;
- head->arg = arg;
+ head->next = NULL;
local_irq_save(flags);
- cpu = smp_processor_id();
- list_add_tail(&head->list, &RCU_nxtlist(cpu));
+ rdp = &__get_cpu_var(rcu_bh_data);
+ *rdp->nxttail = head;
+ rdp->nxttail = &head->next;
local_irq_restore(flags);
}
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
*/
-static void rcu_do_batch(struct list_head *list)
+static void rcu_do_batch(struct rcu_data *rdp)
{
- struct list_head *entry;
- struct rcu_head *head;
-
- while (!list_empty(list)) {
- entry = list->next;
- list_del(entry);
- head = list_entry(entry, struct rcu_head, list);
- head->func(head->arg);
+ struct rcu_head *next, *list;
+ int count = 0;
+
+ list = rdp->donelist;
+ while (list) {
+ next = rdp->donelist = list->next;
+ list->func(list);
+ list = next;
+ if (++count >= maxbatch)
+ break;
}
+ if (!rdp->donelist)
+ rdp->donetail = &rdp->donelist;
+ else
+ tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
}
+/*
+ * Grace period handling:
+ * The grace period handling consists out of two steps:
+ * - A new grace period is started.
+ * This is done by rcu_start_batch. The start is not broadcasted to
+ * all cpus, they must pick this up by comparing rcp->cur with
+ * rdp->quiescbatch. All cpus are recorded in the
+ * rcu_state.cpumask bitmap.
+ * - All cpus must go through a quiescent state.
+ * Since the start of the grace period is not broadcasted, at least two
+ * calls to rcu_check_quiescent_state are required:
+ * The first call just notices that a new grace period is running. The
+ * following calls check if there was a quiescent state since the beginning
+ * of the grace period. If so, it updates rcu_state.cpumask. If
+ * the bitmap is empty, then the grace period is completed.
+ * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
+ * period (if necessary).
+ */
/*
* Register a new batch of callbacks, and start it up if there is currently no
* active batch and the batch to be registered has not already occurred.
- * Caller must hold the rcu_ctrlblk lock.
+ * Caller must hold rcu_state.lock.
*/
-static void rcu_start_batch(long newbatch)
+static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp,
+ int next_pending)
{
- cpumask_t active;
+ if (next_pending)
+ rcp->next_pending = 1;
- if (rcu_batch_before(rcu_ctrlblk.maxbatch, newbatch)) {
- rcu_ctrlblk.maxbatch = newbatch;
+ if (rcp->next_pending &&
+ rcp->completed == rcp->cur) {
+ /* Can't change, since spin lock held. */
+ cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask);
+
+ rcp->next_pending = 0;
+ /* next_pending == 0 must be visible in __rcu_process_callbacks()
+ * before it can see new value of cur.
+ */
+ smp_wmb();
+ rcp->cur++;
}
- if (rcu_batch_before(rcu_ctrlblk.maxbatch, rcu_ctrlblk.curbatch) ||
- !cpus_empty(rcu_ctrlblk.rcu_cpu_mask)) {
- return;
+}
+
+/*
+ * cpu went through a quiescent state since the beginning of the grace period.
+ * Clear it from the cpu mask and complete the grace period if it was the last
+ * cpu. Start another grace period if someone has further entries pending
+ */
+static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp)
+{
+ cpu_clear(cpu, rsp->cpumask);
+ if (cpus_empty(rsp->cpumask)) {
+ /* batch completed ! */
+ rcp->completed = rcp->cur;
+ rcu_start_batch(rcp, rsp, 0);
}
- /* Can't change, since spin lock held. */
- active = nohz_cpu_mask;
- cpus_complement(active);
- cpus_and(rcu_ctrlblk.rcu_cpu_mask, cpu_online_map, active);
}
/*
* switch). If so and if it already hasn't done so in this RCU
* quiescent cycle, then indicate that it has done so.
*/
-static void rcu_check_quiescent_state(void)
+static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
+ struct rcu_state *rsp, struct rcu_data *rdp)
{
- int cpu = smp_processor_id();
+ if (rdp->quiescbatch != rcp->cur) {
+ /* start new grace period: */
+ rdp->qs_pending = 1;
+ rdp->passed_quiesc = 0;
+ rdp->quiescbatch = rcp->cur;
+ return;
+ }
- if (!cpu_isset(cpu, rcu_ctrlblk.rcu_cpu_mask))
+ /* Grace period already completed for this cpu?
+ * qs_pending is checked instead of the actual bitmap to avoid
+ * cacheline trashing.
+ */
+ if (!rdp->qs_pending)
return;
/*
- * Races with local timer interrupt - in the worst case
- * we may miss one quiescent state of that CPU. That is
- * tolerable. So no need to disable interrupts.
+ * Was there a quiescent state since the beginning of the grace
+ * period? If no, then exit and wait for the next call.
*/
- if (RCU_last_qsctr(cpu) == RCU_QSCTR_INVALID) {
- RCU_last_qsctr(cpu) = RCU_qsctr(cpu);
- return;
- }
- if (RCU_qsctr(cpu) == RCU_last_qsctr(cpu))
+ if (!rdp->passed_quiesc)
return;
+ rdp->qs_pending = 0;
- spin_lock(&rcu_ctrlblk.mutex);
- if (!cpu_isset(cpu, rcu_ctrlblk.rcu_cpu_mask))
- goto out_unlock;
-
- cpu_clear(cpu, rcu_ctrlblk.rcu_cpu_mask);
- RCU_last_qsctr(cpu) = RCU_QSCTR_INVALID;
- if (!cpus_empty(rcu_ctrlblk.rcu_cpu_mask))
- goto out_unlock;
-
- rcu_ctrlblk.curbatch++;
- rcu_start_batch(rcu_ctrlblk.maxbatch);
+ spin_lock(&rsp->lock);
+ /*
+ * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
+ * during cpu startup. Ignore the quiescent state.
+ */
+ if (likely(rdp->quiescbatch == rcp->cur))
+ cpu_quiet(rdp->cpu, rcp, rsp);
-out_unlock:
- spin_unlock(&rcu_ctrlblk.mutex);
+ spin_unlock(&rsp->lock);
}
* locking requirements, the list it's pulling from has to belong to a cpu
* which is dead and hence not processing interrupts.
*/
-static void rcu_move_batch(struct list_head *list)
+static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
+ struct rcu_head **tail)
{
- struct list_head *entry;
- int cpu = smp_processor_id();
-
local_irq_disable();
- while (!list_empty(list)) {
- entry = list->next;
- list_del(entry);
- list_add_tail(entry, &RCU_nxtlist(cpu));
- }
+ *this_rdp->nxttail = list;
+ if (list)
+ this_rdp->nxttail = tail;
local_irq_enable();
}
-static void rcu_offline_cpu(int cpu)
+static void __rcu_offline_cpu(struct rcu_data *this_rdp,
+ struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp)
{
/* if the cpu going offline owns the grace period
* we can block indefinitely waiting for it, so flush
* it here
*/
- spin_lock_irq(&rcu_ctrlblk.mutex);
- if (cpus_empty(rcu_ctrlblk.rcu_cpu_mask))
- goto unlock;
-
- cpu_clear(cpu, rcu_ctrlblk.rcu_cpu_mask);
- if (cpus_empty(rcu_ctrlblk.rcu_cpu_mask)) {
- rcu_ctrlblk.curbatch++;
- /* We may avoid calling start batch if
- * we are starting the batch only
- * because of the DEAD CPU (the current
- * CPU will start a new batch anyway for
- * the callbacks we will move to current CPU).
- * However, we will avoid this optimisation
- * for now.
- */
- rcu_start_batch(rcu_ctrlblk.maxbatch);
- }
-unlock:
- spin_unlock_irq(&rcu_ctrlblk.mutex);
+ spin_lock_bh(&rsp->lock);
+ if (rcp->cur != rcp->completed)
+ cpu_quiet(rdp->cpu, rcp, rsp);
+ spin_unlock_bh(&rsp->lock);
+ rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
+ rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
+
+}
+static void rcu_offline_cpu(int cpu)
+{
+ struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
+ struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
+
+ __rcu_offline_cpu(this_rdp, &rcu_ctrlblk, &rcu_state,
+ &per_cpu(rcu_data, cpu));
+ __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &rcu_bh_state,
+ &per_cpu(rcu_bh_data, cpu));
+ put_cpu_var(rcu_data);
+ put_cpu_var(rcu_bh_data);
+ tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
+}
- rcu_move_batch(&RCU_curlist(cpu));
- rcu_move_batch(&RCU_nxtlist(cpu));
+#else
- tasklet_kill_immediate(&RCU_tasklet(cpu), cpu);
+static void rcu_offline_cpu(int cpu)
+{
}
#endif
/*
* This does the RCU processing work from tasklet context.
*/
-static void rcu_process_callbacks(unsigned long unused)
+static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
+ struct rcu_state *rsp, struct rcu_data *rdp)
{
- int cpu = smp_processor_id();
- LIST_HEAD(list);
-
- if (!list_empty(&RCU_curlist(cpu)) &&
- rcu_batch_after(rcu_ctrlblk.curbatch, RCU_batch(cpu))) {
- __list_splice(&RCU_curlist(cpu), &list);
- INIT_LIST_HEAD(&RCU_curlist(cpu));
+ if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
+ *rdp->donetail = rdp->curlist;
+ rdp->donetail = rdp->curtail;
+ rdp->curlist = NULL;
+ rdp->curtail = &rdp->curlist;
}
local_irq_disable();
- if (!list_empty(&RCU_nxtlist(cpu)) && list_empty(&RCU_curlist(cpu))) {
- __list_splice(&RCU_nxtlist(cpu), &RCU_curlist(cpu));
- INIT_LIST_HEAD(&RCU_nxtlist(cpu));
+ if (rdp->nxtlist && !rdp->curlist) {
+ rdp->curlist = rdp->nxtlist;
+ rdp->curtail = rdp->nxttail;
+ rdp->nxtlist = NULL;
+ rdp->nxttail = &rdp->nxtlist;
local_irq_enable();
/*
* start the next batch of callbacks
*/
- spin_lock(&rcu_ctrlblk.mutex);
- RCU_batch(cpu) = rcu_ctrlblk.curbatch + 1;
- rcu_start_batch(RCU_batch(cpu));
- spin_unlock(&rcu_ctrlblk.mutex);
+
+ /* determine batch number */
+ rdp->batch = rcp->cur + 1;
+ /* see the comment and corresponding wmb() in
+ * the rcu_start_batch()
+ */
+ smp_rmb();
+
+ if (!rcp->next_pending) {
+ /* and start it/schedule start if it's a new batch */
+ spin_lock(&rsp->lock);
+ rcu_start_batch(rcp, rsp, 1);
+ spin_unlock(&rsp->lock);
+ }
} else {
local_irq_enable();
}
- rcu_check_quiescent_state();
- if (!list_empty(&list))
- rcu_do_batch(&list);
+ rcu_check_quiescent_state(rcp, rsp, rdp);
+ if (rdp->donelist)
+ rcu_do_batch(rdp);
+}
+
+static void rcu_process_callbacks(unsigned long unused)
+{
+ __rcu_process_callbacks(&rcu_ctrlblk, &rcu_state,
+ &__get_cpu_var(rcu_data));
+ __rcu_process_callbacks(&rcu_bh_ctrlblk, &rcu_bh_state,
+ &__get_cpu_var(rcu_bh_data));
}
void rcu_check_callbacks(int cpu, int user)
{
if (user ||
(idle_cpu(cpu) && !in_softirq() &&
- hardirq_count() <= (1 << HARDIRQ_SHIFT)))
- RCU_qsctr(cpu)++;
- tasklet_schedule(&RCU_tasklet(cpu));
+ hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
+ rcu_qsctr_inc(cpu);
+ rcu_bh_qsctr_inc(cpu);
+ } else if (!in_softirq())
+ rcu_bh_qsctr_inc(cpu);
+ tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
+}
+
+static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ memset(rdp, 0, sizeof(*rdp));
+ rdp->curtail = &rdp->curlist;
+ rdp->nxttail = &rdp->nxtlist;
+ rdp->donetail = &rdp->donelist;
+ rdp->quiescbatch = rcp->completed;
+ rdp->qs_pending = 0;
+ rdp->cpu = cpu;
}
static void __devinit rcu_online_cpu(int cpu)
{
- memset(&per_cpu(rcu_data, cpu), 0, sizeof(struct rcu_data));
- tasklet_init(&RCU_tasklet(cpu), rcu_process_callbacks, 0UL);
- INIT_LIST_HEAD(&RCU_nxtlist(cpu));
- INIT_LIST_HEAD(&RCU_curlist(cpu));
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
+
+ rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
+ rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
+ tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
}
static int __devinit rcu_cpu_notify(struct notifier_block *self,
case CPU_UP_PREPARE:
rcu_online_cpu(cpu);
break;
-#ifdef CONFIG_HOTPLUG_CPU
case CPU_DEAD:
rcu_offline_cpu(cpu);
break;
-#endif
default:
break;
}
register_cpu_notifier(&rcu_nb);
}
+struct rcu_synchronize {
+ struct rcu_head head;
+ struct completion completion;
+};
/* Because of FASTCALL declaration of complete, we use this wrapper */
-static void wakeme_after_rcu(void *completion)
+static void wakeme_after_rcu(struct rcu_head *head)
{
- complete(completion);
+ struct rcu_synchronize *rcu;
+
+ rcu = container_of(head, struct rcu_synchronize, head);
+ complete(&rcu->completion);
}
/**
- * synchronize-kernel - wait until all the CPUs have gone
- * through a "quiescent" state. It may sleep.
+ * synchronize_kernel - 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. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
*/
void synchronize_kernel(void)
{
- struct rcu_head rcu;
- DECLARE_COMPLETION(completion);
+ struct rcu_synchronize rcu;
+ init_completion(&rcu.completion);
/* Will wake me after RCU finished */
- call_rcu(&rcu, wakeme_after_rcu, &completion);
+ call_rcu(&rcu.head, wakeme_after_rcu);
/* Wait for it */
- wait_for_completion(&completion);
+ wait_for_completion(&rcu.completion);
}
-
+module_param(maxbatch, int, 0);
EXPORT_SYMBOL(call_rcu);
+EXPORT_SYMBOL(call_rcu_bh);
EXPORT_SYMBOL(synchronize_kernel);