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authorPaul E. McKenney <paul.mckenney@linaro.org>2012-01-06 14:11:30 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-02-21 09:03:25 -0800
commit486e259340fc4c60474f2c14703e3b3634bb58ca (patch)
tree70a58702194588fa0773463523f72c682785d040 /kernel
parent0bb7b59d6e2b8440cd7097097dd4bbfc4d76ed07 (diff)
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu.h4
-rw-r--r--kernel/rcutiny.c4
-rw-r--r--kernel/rcutree.c29
-rw-r--r--kernel/rcutree.h3
-rw-r--r--kernel/rcutree_plugin.h79
-rw-r--r--kernel/rcutree_trace.c8
6 files changed, 105 insertions, 22 deletions
diff --git a/kernel/rcu.h b/kernel/rcu.h
index aa88baab5f78..a074b0b43fc2 100644
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -76,16 +76,18 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
extern void kfree(const void *);
-static inline void __rcu_reclaim(char *rn, struct rcu_head *head)
+static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
{
unsigned long offset = (unsigned long)head->func;
if (__is_kfree_rcu_offset(offset)) {
RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
kfree((void *)head - offset);
+ return 1;
} else {
RCU_TRACE(trace_rcu_invoke_callback(rn, head));
head->func(head);
+ return 0;
}
}
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 8e00d461911e..4eb34fcc2a75 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -258,7 +258,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* If no RCU callbacks ready to invoke, just return. */
if (&rcp->rcucblist == rcp->donetail) {
- RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
+ RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
ACCESS_ONCE(rcp->rcucblist),
need_resched(),
@@ -269,7 +269,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
- RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
+ RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 570f7530f4b3..acf2d67ad2f4 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1261,6 +1261,7 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp)
*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 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp)
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 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
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 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
*/
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 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
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 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
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 invoke_rcu_core(void)
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 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
*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 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
*/
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 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
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);
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index fddff92d6676..af2af3cc5e65 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -265,7 +265,8 @@ struct rcu_data {
*/
struct rcu_head *nxtlist;
struct rcu_head **nxttail[RCU_NEXT_SIZE];
- long qlen; /* # of queued callbacks */
+ long qlen_lazy; /* # of lazy queued callbacks */
+ long qlen; /* # of queued callbacks, incl lazy */
long qlen_last_fqs_check;
/* qlen at last check for QS forcing */
unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 3680b6b35bf3..7adf232bb66b 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -671,10 +671,24 @@ static void rcu_preempt_do_callbacks(void)
*/
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
- __call_rcu(head, func, &rcu_preempt_state);
+ __call_rcu(head, func, &rcu_preempt_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu);
+/*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks. Until then, this
+ * function may only be called from __kfree_rcu().
+ */
+void kfree_call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ __call_rcu(head, func, &rcu_preempt_state, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
@@ -1065,6 +1079,22 @@ static void rcu_preempt_process_callbacks(void)
}
/*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks. Until then, this
+ * function may only be called from __kfree_rcu().
+ *
+ * Because there is no preemptible RCU, we use RCU-sched instead.
+ */
+void kfree_call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ __call_rcu(head, func, &rcu_sched_state, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
+/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
* But because preemptible RCU does not exist, map to rcu-sched.
*/
@@ -2052,6 +2082,48 @@ int rcu_needs_cpu(int cpu)
}
/*
+ * Does the specified flavor of RCU have non-lazy callbacks pending on
+ * the specified CPU? Both RCU flavor and CPU are specified by the
+ * rcu_data structure.
+ */
+static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
+{
+ return rdp->qlen != rdp->qlen_lazy;
+}
+
+#ifdef CONFIG_TREE_PREEMPT_RCU
+
+/*
+ * Are there non-lazy RCU-preempt callbacks? (There cannot be if there
+ * is no RCU-preempt in the kernel.)
+ */
+static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
+
+ return __rcu_cpu_has_nonlazy_callbacks(rdp);
+}
+
+#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
+{
+ return 0;
+}
+
+#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+/*
+ * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
+ */
+static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
+{
+ return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
+ __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
+ rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
+}
+
+/*
* Timer handler used to force CPU to start pushing its remaining RCU
* callbacks in the case where it entered dyntick-idle mode with callbacks
* pending. The hander doesn't really need to do anything because the
@@ -2149,8 +2221,9 @@ static void rcu_prepare_for_idle(int cpu)
trace_rcu_prep_idle("Dyntick with callbacks");
per_cpu(rcu_dyntick_drain, cpu) = 0;
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
- hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
- rcu_idle_gp_wait, HRTIMER_MODE_REL);
+ if (rcu_cpu_has_nonlazy_callbacks(cpu))
+ hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
+ rcu_idle_gp_wait, HRTIMER_MODE_REL);
return; /* Nothing more to do immediately. */
} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
/* We have hit the limit, so time to give up. */
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 654cfe67f0d1..db0987c1e1bd 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -73,8 +73,8 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
- seq_printf(m, " ql=%ld qs=%c%c%c%c",
- rdp->qlen,
+ seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c",
+ rdp->qlen_lazy, rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@@ -145,7 +145,7 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
- seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
+ seq_printf(m, ",%ld,%ld,\"%c%c%c%c\"", rdp->qlen_lazy, rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@@ -168,7 +168,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
{
seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\",");
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
- seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
+ seq_puts(m, "\"of\",\"ri\",\"qll\",\"ql\",\"qs\"");
#ifdef CONFIG_RCU_BOOST
seq_puts(m, "\"kt\",\"ktl\"");
#endif /* #ifdef CONFIG_RCU_BOOST */