rcu: Avoid waking up CPUs having only kfree_rcu() callbacks
When CONFIG_RCU_FAST_NO_HZ is enabled, RCU will allow a given CPU to
enter dyntick-idle mode even if it still has RCU callbacks queued.
RCU avoids system hangs in this case by scheduling a timer for several
jiffies in the future. However, if all of the callbacks on that CPU
are from kfree_rcu(), there is no reason to wake the CPU up, as it is
not a problem to defer freeing of memory.
This commit therefore tracks the number of callbacks on a given CPU
that are from kfree_rcu(), and avoids scheduling the timer if all of
a given CPU's callbacks are from kfree_rcu().
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 570f753..acf2d67 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1261,6 +1261,7 @@
*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+ receive_rdp->qlen_lazy += rdp->qlen_lazy;
receive_rdp->qlen += rdp->qlen;
receive_rdp->n_cbs_adopted += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
@@ -1268,6 +1269,7 @@
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
+ rdp->qlen_lazy = 0;
rdp->qlen = 0;
}
@@ -1368,11 +1370,11 @@
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
- int bl, count;
+ int bl, count, count_lazy;
/* If no callbacks are ready, just return.*/
if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
- trace_rcu_batch_start(rsp->name, 0, 0);
+ trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
@@ -1385,7 +1387,7 @@
*/
local_irq_save(flags);
bl = rdp->blimit;
- trace_rcu_batch_start(rsp->name, rdp->qlen, bl);
+ trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
@@ -1396,12 +1398,13 @@
local_irq_restore(flags);
/* Invoke callbacks. */
- count = 0;
+ count = count_lazy = 0;
while (list) {
next = list->next;
prefetch(next);
debug_rcu_head_unqueue(list);
- __rcu_reclaim(rsp->name, list);
+ if (__rcu_reclaim(rsp->name, list))
+ count_lazy++;
list = next;
/* Stop only if limit reached and CPU has something to do. */
if (++count >= bl &&
@@ -1416,6 +1419,7 @@
rcu_is_callbacks_kthread());
/* Update count, and requeue any remaining callbacks. */
+ rdp->qlen_lazy -= count_lazy;
rdp->qlen -= count;
rdp->n_cbs_invoked += count;
if (list != NULL) {
@@ -1702,7 +1706,7 @@
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
- struct rcu_state *rsp)
+ struct rcu_state *rsp, bool lazy)
{
unsigned long flags;
struct rcu_data *rdp;
@@ -1727,12 +1731,14 @@
*rdp->nxttail[RCU_NEXT_TAIL] = head;
rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
rdp->qlen++;
+ if (lazy)
+ rdp->qlen_lazy++;
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
- rdp->qlen);
+ rdp->qlen_lazy, rdp->qlen);
else
- trace_rcu_callback(rsp->name, head, rdp->qlen);
+ trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
/* If interrupts were disabled, don't dive into RCU core. */
if (irqs_disabled_flags(flags)) {
@@ -1779,16 +1785,16 @@
*/
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
- __call_rcu(head, func, &rcu_sched_state);
+ __call_rcu(head, func, &rcu_sched_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);
/*
- * Queue an RCU for invocation after a quicker grace period.
+ * Queue an RCU callback for invocation after a quicker grace period.
*/
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
- __call_rcu(head, func, &rcu_bh_state);
+ __call_rcu(head, func, &rcu_bh_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
@@ -2036,6 +2042,7 @@
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
+ rdp->qlen_lazy = 0;
rdp->qlen = 0;
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);