raw_spin_unlock_rcu_node(rnp);
}
-/**
- * call_rcu() - Queue an RCU callback for invocation after a grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual callback function to be invoked after the grace period
- *
- * The callback function will be invoked some time after a full grace
- * period elapses, in other words after all pre-existing RCU read-side
- * critical sections have completed. However, the callback function
- * might well execute concurrently with RCU read-side critical sections
- * that started after call_rcu() was invoked.
- *
- * RCU read-side critical sections are delimited by rcu_read_lock()
- * and rcu_read_unlock(), and may be nested. In addition, but only in
- * v5.0 and later, 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 all CPUs must agree that the grace period extended beyond
- * all pre-existing RCU read-side critical section. On systems with more
- * than one CPU, this means that when "func()" is invoked, 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 call_rcu(). It also means that each CPU executing an RCU read-side
- * critical section that continues beyond the start of "func()" must have
- * executed a memory barrier after the call_rcu() but 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 call_rcu() and CPU B invoked the
- * resulting RCU callback function "func()", then both CPU A and CPU B are
- * guaranteed to execute a full memory barrier during the time interval
- * between the call to call_rcu() and the invocation of "func()" -- even
- * if CPU A and CPU B are the same CPU (but again only if the system has
- * more than one CPU).
- *
- * Implementation of these memory-ordering guarantees is described here:
- * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
- */
-void call_rcu(struct rcu_head *head, rcu_callback_t func)
+static void
+__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
{
static atomic_t doublefrees;
unsigned long flags;
}
check_cb_ovld(rdp);
- if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
+ if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
return; // Enqueued onto ->nocb_bypass, so just leave.
// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
rcu_segcblist_enqueue(&rdp->cblist, head);
local_irq_restore(flags);
}
}
-EXPORT_SYMBOL_GPL(call_rcu);
+#ifdef CONFIG_RCU_LAZY
+/**
+ * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
+ * flush all lazy callbacks (including the new one) to the main ->cblist while
+ * doing so.
+ *
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed.
+ *
+ * Use this API instead of call_rcu() if you don't want the callback to be
+ * invoked after very long periods of time, which can happen on systems without
+ * memory pressure and on systems which are lightly loaded or mostly idle.
+ * This function will cause callbacks to be invoked sooner than later at the
+ * expense of extra power. Other than that, this function is identical to, and
+ * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory
+ * ordering and other functionality.
+ */
+void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
+{
+ return __call_rcu_common(head, func, false);
+}
+EXPORT_SYMBOL_GPL(call_rcu_hurry);
+#endif
+
+/**
+ * call_rcu() - Queue an RCU callback for invocation after a grace period.
+ * By default the callbacks are 'lazy' and are kept hidden from the main
+ * ->cblist to prevent starting of grace periods too soon.
+ * If you desire grace periods to start very soon, use call_rcu_hurry().
+ *
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed. However, the callback function
+ * might well execute concurrently with RCU read-side critical sections
+ * that started after call_rcu() was invoked.
+ *
+ * RCU read-side critical sections are delimited by rcu_read_lock()
+ * and rcu_read_unlock(), and may be nested. In addition, but only in
+ * v5.0 and later, 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 all CPUs must agree that the grace period extended beyond
+ * all pre-existing RCU read-side critical section. On systems with more
+ * than one CPU, this means that when "func()" is invoked, 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 call_rcu(). It also means that each CPU executing an RCU read-side
+ * critical section that continues beyond the start of "func()" must have
+ * executed a memory barrier after the call_rcu() but 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 call_rcu() and CPU B invoked the
+ * resulting RCU callback function "func()", then both CPU A and CPU B are
+ * guaranteed to execute a full memory barrier during the time interval
+ * between the call to call_rcu() and the invocation of "func()" -- even
+ * if CPU A and CPU B are the same CPU (but again only if the system has
+ * more than one CPU).
+ *
+ * Implementation of these memory-ordering guarantees is described here:
+ * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
+ */
+void call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+ return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
+}
+EXPORT_SYMBOL_GPL(call_rcu);
/* Maximum number of jiffies to wait before draining a batch. */
#define KFREE_DRAIN_JIFFIES (5 * HZ)
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
- wait_rcu_gp(call_rcu);
+ wait_rcu_gp(call_rcu_hurry);
return;
}
* if it's fully lazy.
*/
was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist);
- WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist);
if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
atomic_inc(&rcu_state.barrier_cpu_count);
my_rdp = this_cpu_ptr(&rcu_data);
my_rnp = my_rdp->mynode;
rcu_nocb_lock(my_rdp); /* irqs already disabled. */
- WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false));
raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
/* Leverage recent GPs and set GP for new callbacks. */
needwake = rcu_advance_cbs(my_rnp, rdp) ||
return __wake_nocb_gp(rdp_gp, rdp, force, flags);
}
+/*
+ * LAZY_FLUSH_JIFFIES decides the maximum amount of time that
+ * can elapse before lazy callbacks are flushed. Lazy callbacks
+ * could be flushed much earlier for a number of other reasons
+ * however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are
+ * left unsubmitted to RCU after those many jiffies.
+ */
+#define LAZY_FLUSH_JIFFIES (10 * HZ)
+static unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES;
+
+#ifdef CONFIG_RCU_LAZY
+// To be called only from test code.
+void rcu_lazy_set_jiffies_till_flush(unsigned long jif)
+{
+ jiffies_till_flush = jif;
+}
+EXPORT_SYMBOL(rcu_lazy_set_jiffies_till_flush);
+
+unsigned long rcu_lazy_get_jiffies_till_flush(void)
+{
+ return jiffies_till_flush;
+}
+EXPORT_SYMBOL(rcu_lazy_get_jiffies_till_flush);
+#endif
+
/*
* Arrange to wake the GP kthread for this NOCB group at some future
* time when it is safe to do so.
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
/*
- * Bypass wakeup overrides previous deferments. In case
- * of callback storm, no need to wake up too early.
+ * Bypass wakeup overrides previous deferments. In case of
+ * callback storms, no need to wake up too early.
*/
- if (waketype == RCU_NOCB_WAKE_BYPASS) {
+ if (waketype == RCU_NOCB_WAKE_LAZY &&
+ rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
+ mod_timer(&rdp_gp->nocb_timer, jiffies + jiffies_till_flush);
+ WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
+ } else if (waketype == RCU_NOCB_WAKE_BYPASS) {
mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
} else {
* proves to be initially empty, just return false because the no-CB GP
* kthread may need to be awakened in this case.
*
+ * Return true if there was something to be flushed and it succeeded, otherwise
+ * false.
+ *
* Note that this function always returns true if rhp is NULL.
*/
static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- unsigned long j)
+ unsigned long j, bool lazy)
{
struct rcu_cblist rcl;
/* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
if (rhp)
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
- rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
+
+ /*
+ * If the new CB requested was a lazy one, queue it onto the main
+ * ->cblist so we can take advantage of a sooner grade period.
+ */
+ if (lazy && rhp) {
+ rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, NULL);
+ rcu_cblist_enqueue(&rcl, rhp);
+ WRITE_ONCE(rdp->lazy_len, 0);
+ } else {
+ rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
+ WRITE_ONCE(rdp->lazy_len, 0);
+ }
+
rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
WRITE_ONCE(rdp->nocb_bypass_first, j);
rcu_nocb_bypass_unlock(rdp);
* Note that this function always returns true if rhp is NULL.
*/
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- unsigned long j)
+ unsigned long j, bool lazy)
{
if (!rcu_rdp_is_offloaded(rdp))
return true;
rcu_lockdep_assert_cblist_protected(rdp);
rcu_nocb_bypass_lock(rdp);
- return rcu_nocb_do_flush_bypass(rdp, rhp, j);
+ return rcu_nocb_do_flush_bypass(rdp, rhp, j, lazy);
}
/*
if (!rcu_rdp_is_offloaded(rdp) ||
!rcu_nocb_bypass_trylock(rdp))
return;
- WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
+ WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j, false));
}
/*
* there is only one CPU in operation.
*/
static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- bool *was_alldone, unsigned long flags)
+ bool *was_alldone, unsigned long flags,
+ bool lazy)
{
unsigned long c;
unsigned long cur_gp_seq;
unsigned long j = jiffies;
long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ bool bypass_is_lazy = (ncbs == READ_ONCE(rdp->lazy_len));
lockdep_assert_irqs_disabled();
// If there hasn't yet been all that many ->cblist enqueues
// this jiffy, tell the caller to enqueue onto ->cblist. But flush
// ->nocb_bypass first.
- if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
+ // Lazy CBs throttle this back and do immediate bypass queuing.
+ if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy && !lazy) {
rcu_nocb_lock(rdp);
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
if (*was_alldone)
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstQ"));
- WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
+
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j, false));
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
return false; // Caller must enqueue the callback.
}
// If ->nocb_bypass has been used too long or is too full,
// flush ->nocb_bypass to ->cblist.
- if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
+ if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) ||
+ (ncbs && bypass_is_lazy &&
+ (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush))) ||
ncbs >= qhimark) {
rcu_nocb_lock(rdp);
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
- if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
+ if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy)) {
if (*was_alldone)
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstQ"));
ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
+
+ if (lazy)
+ WRITE_ONCE(rdp->lazy_len, rdp->lazy_len + 1);
+
if (!ncbs) {
WRITE_ONCE(rdp->nocb_bypass_first, j);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
}
rcu_nocb_bypass_unlock(rdp);
smp_mb(); /* Order enqueue before wake. */
- if (ncbs) {
+ // A wake up of the grace period kthread or timer adjustment
+ // needs to be done only if:
+ // 1. Bypass list was fully empty before (this is the first
+ // bypass list entry), or:
+ // 2. Both of these conditions are met:
+ // a. The bypass list previously had only lazy CBs, and:
+ // b. The new CB is non-lazy.
+ if (ncbs && (!bypass_is_lazy || lazy)) {
local_irq_restore(flags);
} else {
// No-CBs GP kthread might be indefinitely asleep, if so, wake.
unsigned long flags)
__releases(rdp->nocb_lock)
{
+ long bypass_len;
unsigned long cur_gp_seq;
unsigned long j;
+ long lazy_len;
long len;
struct task_struct *t;
}
// Need to actually to a wakeup.
len = rcu_segcblist_n_cbs(&rdp->cblist);
+ bypass_len = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ lazy_len = READ_ONCE(rdp->lazy_len);
if (was_alldone) {
rdp->qlen_last_fqs_check = len;
- if (!irqs_disabled_flags(flags)) {
+ // Only lazy CBs in bypass list
+ if (lazy_len && bypass_len == lazy_len) {
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
+ TPS("WakeLazy"));
+ } else if (!irqs_disabled_flags(flags)) {
/* ... if queue was empty ... */
rcu_nocb_unlock_irqrestore(rdp, flags);
wake_nocb_gp(rdp, false);
static void nocb_gp_wait(struct rcu_data *my_rdp)
{
bool bypass = false;
- long bypass_ncbs;
int __maybe_unused cpu = my_rdp->cpu;
unsigned long cur_gp_seq;
unsigned long flags;
bool gotcbs = false;
unsigned long j = jiffies;
+ bool lazy = false;
bool needwait_gp = false; // This prevents actual uninitialized use.
bool needwake;
bool needwake_gp;
* won't be ignored for long.
*/
list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) {
+ long bypass_ncbs;
+ bool flush_bypass = false;
+ long lazy_ncbs;
+
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
rcu_nocb_lock_irqsave(rdp, flags);
lockdep_assert_held(&rdp->nocb_lock);
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
- if (bypass_ncbs &&
+ lazy_ncbs = READ_ONCE(rdp->lazy_len);
+
+ if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
+ (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) ||
+ bypass_ncbs > 2 * qhimark)) {
+ flush_bypass = true;
+ } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
bypass_ncbs > 2 * qhimark)) {
- // Bypass full or old, so flush it.
- (void)rcu_nocb_try_flush_bypass(rdp, j);
- bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ flush_bypass = true;
} else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
rcu_nocb_unlock_irqrestore(rdp, flags);
continue; /* No callbacks here, try next. */
}
+
+ if (flush_bypass) {
+ // Bypass full or old, so flush it.
+ (void)rcu_nocb_try_flush_bypass(rdp, j);
+ bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ lazy_ncbs = READ_ONCE(rdp->lazy_len);
+ }
+
if (bypass_ncbs) {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("Bypass"));
- bypass = true;
+ bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass"));
+ if (bypass_ncbs == lazy_ncbs)
+ lazy = true;
+ else
+ bypass = true;
}
rnp = rdp->mynode;
my_rdp->nocb_gp_gp = needwait_gp;
my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
- if (bypass && !rcu_nocb_poll) {
- // At least one child with non-empty ->nocb_bypass, so set
- // timer in order to avoid stranding its callbacks.
- wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
- TPS("WakeBypassIsDeferred"));
+ // At least one child with non-empty ->nocb_bypass, so set
+ // timer in order to avoid stranding its callbacks.
+ if (!rcu_nocb_poll) {
+ // If bypass list only has lazy CBs. Add a deferred lazy wake up.
+ if (lazy && !bypass) {
+ wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY,
+ TPS("WakeLazyIsDeferred"));
+ // Otherwise add a deferred bypass wake up.
+ } else if (bypass) {
+ wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
+ TPS("WakeBypassIsDeferred"));
+ }
}
+
if (rcu_nocb_poll) {
/* Polling, so trace if first poll in the series. */
if (gotcbs)
* return false, which means that future calls to rcu_nocb_try_bypass()
* will refuse to put anything into the bypass.
*/
- WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
/*
* Start with invoking rcu_core() early. This way if the current thread
* happens to preempt an ongoing call to rcu_core() in the middle,
raw_spin_lock_init(&rdp->nocb_gp_lock);
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
rcu_cblist_init(&rdp->nocb_bypass);
+ WRITE_ONCE(rdp->lazy_len, 0);
mutex_init(&rdp->nocb_gp_kthread_mutex);
}
}
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- unsigned long j)
+ unsigned long j, bool lazy)
{
return true;
}
static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- bool *was_alldone, unsigned long flags)
+ bool *was_alldone, unsigned long flags, bool lazy)
{
return false;
}
projects / linux-2.6-microblaze.git / commitdiff