static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]()
So here's a boot tested patch on top of Jason's series that does
all the cleanups I talked about and turns jump labels into a
more intuitive to use facility. It should also address the
various misconceptions and confusions that surround jump labels.
Typical usage scenarios:
#include <linux/static_key.h>
struct static_key key = STATIC_KEY_INIT_TRUE;
if (static_key_false(&key))
do unlikely code
else
do likely code
Or:
if (static_key_true(&key))
do likely code
else
do unlikely code
The static key is modified via:
static_key_slow_inc(&key);
...
static_key_slow_dec(&key);
The 'slow' prefix makes it abundantly clear that this is an
expensive operation.
I've updated all in-kernel code to use this everywhere. Note
that I (intentionally) have not pushed through the rename
blindly through to the lowest levels: the actual jump-label
patching arch facility should be named like that, so we want to
decouple jump labels from the static-key facility a bit.
On non-jump-label enabled architectures static keys default to
likely()/unlikely() branches.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: a.p.zijlstra@chello.nl
Cc: mathieu.desnoyers@efficios.com
Cc: davem@davemloft.net
Cc: ddaney.cavm@gmail.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7c3b9de..5e0f8bb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -128,7 +128,7 @@
* perf_sched_events : >0 events exist
* perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu
*/
-struct jump_label_key_deferred perf_sched_events __read_mostly;
+struct static_key_deferred perf_sched_events __read_mostly;
static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
static atomic_t nr_mmap_events __read_mostly;
@@ -2769,7 +2769,7 @@
if (!event->parent) {
if (event->attach_state & PERF_ATTACH_TASK)
- jump_label_dec_deferred(&perf_sched_events);
+ static_key_slow_dec_deferred(&perf_sched_events);
if (event->attr.mmap || event->attr.mmap_data)
atomic_dec(&nr_mmap_events);
if (event->attr.comm)
@@ -2780,7 +2780,7 @@
put_callchain_buffers();
if (is_cgroup_event(event)) {
atomic_dec(&per_cpu(perf_cgroup_events, event->cpu));
- jump_label_dec_deferred(&perf_sched_events);
+ static_key_slow_dec_deferred(&perf_sched_events);
}
}
@@ -4982,7 +4982,7 @@
return err;
}
-struct jump_label_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
+struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
static void sw_perf_event_destroy(struct perf_event *event)
{
@@ -4990,7 +4990,7 @@
WARN_ON(event->parent);
- jump_label_dec(&perf_swevent_enabled[event_id]);
+ static_key_slow_dec(&perf_swevent_enabled[event_id]);
swevent_hlist_put(event);
}
@@ -5020,7 +5020,7 @@
if (err)
return err;
- jump_label_inc(&perf_swevent_enabled[event_id]);
+ static_key_slow_inc(&perf_swevent_enabled[event_id]);
event->destroy = sw_perf_event_destroy;
}
@@ -5843,7 +5843,7 @@
if (!event->parent) {
if (event->attach_state & PERF_ATTACH_TASK)
- jump_label_inc(&perf_sched_events.key);
+ static_key_slow_inc(&perf_sched_events.key);
if (event->attr.mmap || event->attr.mmap_data)
atomic_inc(&nr_mmap_events);
if (event->attr.comm)
@@ -6081,7 +6081,7 @@
* - that may need work on context switch
*/
atomic_inc(&per_cpu(perf_cgroup_events, event->cpu));
- jump_label_inc(&perf_sched_events.key);
+ static_key_slow_inc(&perf_sched_events.key);
}
/*
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 543782e..bf9dcad 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -12,7 +12,7 @@
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/err.h>
-#include <linux/jump_label.h>
+#include <linux/static_key.h>
#ifdef HAVE_JUMP_LABEL
@@ -29,10 +29,11 @@
mutex_unlock(&jump_label_mutex);
}
-bool jump_label_enabled(struct jump_label_key *key)
+bool static_key_enabled(struct static_key *key)
{
- return !!atomic_read(&key->enabled);
+ return (atomic_read(&key->enabled) > 0);
}
+EXPORT_SYMBOL_GPL(static_key_enabled);
static int jump_label_cmp(const void *a, const void *b)
{
@@ -58,22 +59,26 @@
sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
}
-static void jump_label_update(struct jump_label_key *key, int enable);
+static void jump_label_update(struct static_key *key, int enable);
-void jump_label_inc(struct jump_label_key *key)
+void static_key_slow_inc(struct static_key *key)
{
if (atomic_inc_not_zero(&key->enabled))
return;
jump_label_lock();
- if (atomic_read(&key->enabled) == 0)
- jump_label_update(key, JUMP_LABEL_ENABLE);
+ if (atomic_read(&key->enabled) == 0) {
+ if (!jump_label_get_branch_default(key))
+ jump_label_update(key, JUMP_LABEL_ENABLE);
+ else
+ jump_label_update(key, JUMP_LABEL_DISABLE);
+ }
atomic_inc(&key->enabled);
jump_label_unlock();
}
-EXPORT_SYMBOL_GPL(jump_label_inc);
+EXPORT_SYMBOL_GPL(static_key_slow_inc);
-static void __jump_label_dec(struct jump_label_key *key,
+static void __static_key_slow_dec(struct static_key *key,
unsigned long rate_limit, struct delayed_work *work)
{
if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
@@ -85,32 +90,35 @@
if (rate_limit) {
atomic_inc(&key->enabled);
schedule_delayed_work(work, rate_limit);
- } else
- jump_label_update(key, JUMP_LABEL_DISABLE);
-
+ } else {
+ if (!jump_label_get_branch_default(key))
+ jump_label_update(key, JUMP_LABEL_DISABLE);
+ else
+ jump_label_update(key, JUMP_LABEL_ENABLE);
+ }
jump_label_unlock();
}
-EXPORT_SYMBOL_GPL(jump_label_dec);
static void jump_label_update_timeout(struct work_struct *work)
{
- struct jump_label_key_deferred *key =
- container_of(work, struct jump_label_key_deferred, work.work);
- __jump_label_dec(&key->key, 0, NULL);
+ struct static_key_deferred *key =
+ container_of(work, struct static_key_deferred, work.work);
+ __static_key_slow_dec(&key->key, 0, NULL);
}
-void jump_label_dec(struct jump_label_key *key)
+void static_key_slow_dec(struct static_key *key)
{
- __jump_label_dec(key, 0, NULL);
+ __static_key_slow_dec(key, 0, NULL);
}
+EXPORT_SYMBOL_GPL(static_key_slow_dec);
-void jump_label_dec_deferred(struct jump_label_key_deferred *key)
+void static_key_slow_dec_deferred(struct static_key_deferred *key)
{
- __jump_label_dec(&key->key, key->timeout, &key->work);
+ __static_key_slow_dec(&key->key, key->timeout, &key->work);
}
+EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
-
-void jump_label_rate_limit(struct jump_label_key_deferred *key,
+void jump_label_rate_limit(struct static_key_deferred *key,
unsigned long rl)
{
key->timeout = rl;
@@ -153,7 +161,7 @@
arch_jump_label_transform(entry, type);
}
-static void __jump_label_update(struct jump_label_key *key,
+static void __jump_label_update(struct static_key *key,
struct jump_entry *entry,
struct jump_entry *stop, int enable)
{
@@ -170,27 +178,40 @@
}
}
+static enum jump_label_type jump_label_type(struct static_key *key)
+{
+ bool true_branch = jump_label_get_branch_default(key);
+ bool state = static_key_enabled(key);
+
+ if ((!true_branch && state) || (true_branch && !state))
+ return JUMP_LABEL_ENABLE;
+
+ return JUMP_LABEL_DISABLE;
+}
+
void __init jump_label_init(void)
{
struct jump_entry *iter_start = __start___jump_table;
struct jump_entry *iter_stop = __stop___jump_table;
- struct jump_label_key *key = NULL;
+ struct static_key *key = NULL;
struct jump_entry *iter;
jump_label_lock();
jump_label_sort_entries(iter_start, iter_stop);
for (iter = iter_start; iter < iter_stop; iter++) {
- struct jump_label_key *iterk;
+ struct static_key *iterk;
- iterk = (struct jump_label_key *)(unsigned long)iter->key;
- arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
- JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
+ iterk = (struct static_key *)(unsigned long)iter->key;
+ arch_jump_label_transform_static(iter, jump_label_type(iterk));
if (iterk == key)
continue;
key = iterk;
- key->entries = iter;
+ /*
+ * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
+ */
+ *((unsigned long *)&key->entries) += (unsigned long)iter;
#ifdef CONFIG_MODULES
key->next = NULL;
#endif
@@ -200,8 +221,8 @@
#ifdef CONFIG_MODULES
-struct jump_label_mod {
- struct jump_label_mod *next;
+struct static_key_mod {
+ struct static_key_mod *next;
struct jump_entry *entries;
struct module *mod;
};
@@ -221,9 +242,9 @@
start, end);
}
-static void __jump_label_mod_update(struct jump_label_key *key, int enable)
+static void __jump_label_mod_update(struct static_key *key, int enable)
{
- struct jump_label_mod *mod = key->next;
+ struct static_key_mod *mod = key->next;
while (mod) {
struct module *m = mod->mod;
@@ -254,11 +275,7 @@
return;
for (iter = iter_start; iter < iter_stop; iter++) {
- struct jump_label_key *iterk;
-
- iterk = (struct jump_label_key *)(unsigned long)iter->key;
- arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
- JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
+ arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
}
}
@@ -267,8 +284,8 @@
struct jump_entry *iter_start = mod->jump_entries;
struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
struct jump_entry *iter;
- struct jump_label_key *key = NULL;
- struct jump_label_mod *jlm;
+ struct static_key *key = NULL;
+ struct static_key_mod *jlm;
/* if the module doesn't have jump label entries, just return */
if (iter_start == iter_stop)
@@ -277,28 +294,30 @@
jump_label_sort_entries(iter_start, iter_stop);
for (iter = iter_start; iter < iter_stop; iter++) {
- if (iter->key == (jump_label_t)(unsigned long)key)
+ struct static_key *iterk;
+
+ iterk = (struct static_key *)(unsigned long)iter->key;
+ if (iterk == key)
continue;
- key = (struct jump_label_key *)(unsigned long)iter->key;
-
+ key = iterk;
if (__module_address(iter->key) == mod) {
- atomic_set(&key->enabled, 0);
- key->entries = iter;
+ /*
+ * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
+ */
+ *((unsigned long *)&key->entries) += (unsigned long)iter;
key->next = NULL;
continue;
}
-
- jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
+ jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
if (!jlm)
return -ENOMEM;
-
jlm->mod = mod;
jlm->entries = iter;
jlm->next = key->next;
key->next = jlm;
- if (jump_label_enabled(key))
+ if (jump_label_type(key) == JUMP_LABEL_ENABLE)
__jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
}
@@ -310,14 +329,14 @@
struct jump_entry *iter_start = mod->jump_entries;
struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
struct jump_entry *iter;
- struct jump_label_key *key = NULL;
- struct jump_label_mod *jlm, **prev;
+ struct static_key *key = NULL;
+ struct static_key_mod *jlm, **prev;
for (iter = iter_start; iter < iter_stop; iter++) {
if (iter->key == (jump_label_t)(unsigned long)key)
continue;
- key = (struct jump_label_key *)(unsigned long)iter->key;
+ key = (struct static_key *)(unsigned long)iter->key;
if (__module_address(iter->key) == mod)
continue;
@@ -419,9 +438,10 @@
return ret;
}
-static void jump_label_update(struct jump_label_key *key, int enable)
+static void jump_label_update(struct static_key *key, int enable)
{
- struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
+ struct jump_entry *stop = __stop___jump_table;
+ struct jump_entry *entry = jump_label_get_entries(key);
#ifdef CONFIG_MODULES
struct module *mod = __module_address((unsigned long)key);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5255c9d..112c682 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -162,13 +162,13 @@
#ifdef HAVE_JUMP_LABEL
-#define jump_label_key__true jump_label_key_enabled
-#define jump_label_key__false jump_label_key_disabled
+#define jump_label_key__true STATIC_KEY_INIT_TRUE
+#define jump_label_key__false STATIC_KEY_INIT_FALSE
#define SCHED_FEAT(name, enabled) \
jump_label_key__##enabled ,
-struct jump_label_key sched_feat_keys[__SCHED_FEAT_NR] = {
+struct static_key sched_feat_keys[__SCHED_FEAT_NR] = {
#include "features.h"
};
@@ -176,14 +176,14 @@
static void sched_feat_disable(int i)
{
- if (jump_label_enabled(&sched_feat_keys[i]))
- jump_label_dec(&sched_feat_keys[i]);
+ if (static_key_enabled(&sched_feat_keys[i]))
+ static_key_slow_dec(&sched_feat_keys[i]);
}
static void sched_feat_enable(int i)
{
- if (!jump_label_enabled(&sched_feat_keys[i]))
- jump_label_inc(&sched_feat_keys[i]);
+ if (!static_key_enabled(&sched_feat_keys[i]))
+ static_key_slow_inc(&sched_feat_keys[i]);
}
#else
static void sched_feat_disable(int i) { };
@@ -894,7 +894,7 @@
delta -= irq_delta;
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
- if (static_branch((¶virt_steal_rq_enabled))) {
+ if (static_key_false((¶virt_steal_rq_enabled))) {
u64 st;
steal = paravirt_steal_clock(cpu_of(rq));
@@ -2756,7 +2756,7 @@
static __always_inline bool steal_account_process_tick(void)
{
#ifdef CONFIG_PARAVIRT
- if (static_branch(¶virt_steal_enabled)) {
+ if (static_key_false(¶virt_steal_enabled)) {
u64 steal, st = 0;
steal = paravirt_steal_clock(smp_processor_id());
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c6414f..423547a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1399,20 +1399,20 @@
#ifdef CONFIG_CFS_BANDWIDTH
#ifdef HAVE_JUMP_LABEL
-static struct jump_label_key __cfs_bandwidth_used;
+static struct static_key __cfs_bandwidth_used;
static inline bool cfs_bandwidth_used(void)
{
- return static_branch(&__cfs_bandwidth_used);
+ return static_key_false(&__cfs_bandwidth_used);
}
void account_cfs_bandwidth_used(int enabled, int was_enabled)
{
/* only need to count groups transitioning between enabled/!enabled */
if (enabled && !was_enabled)
- jump_label_inc(&__cfs_bandwidth_used);
+ static_key_slow_inc(&__cfs_bandwidth_used);
else if (!enabled && was_enabled)
- jump_label_dec(&__cfs_bandwidth_used);
+ static_key_slow_dec(&__cfs_bandwidth_used);
}
#else /* HAVE_JUMP_LABEL */
static bool cfs_bandwidth_used(void)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 98c0c26..b4cd6d8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -611,7 +611,7 @@
* Tunables that become constants when CONFIG_SCHED_DEBUG is off:
*/
#ifdef CONFIG_SCHED_DEBUG
-# include <linux/jump_label.h>
+# include <linux/static_key.h>
# define const_debug __read_mostly
#else
# define const_debug const
@@ -630,18 +630,18 @@
#undef SCHED_FEAT
#if defined(CONFIG_SCHED_DEBUG) && defined(HAVE_JUMP_LABEL)
-static __always_inline bool static_branch__true(struct jump_label_key *key)
+static __always_inline bool static_branch__true(struct static_key *key)
{
- return likely(static_branch(key)); /* Not out of line branch. */
+ return static_key_true(key); /* Not out of line branch. */
}
-static __always_inline bool static_branch__false(struct jump_label_key *key)
+static __always_inline bool static_branch__false(struct static_key *key)
{
- return unlikely(static_branch(key)); /* Out of line branch. */
+ return static_key_false(key); /* Out of line branch. */
}
#define SCHED_FEAT(name, enabled) \
-static __always_inline bool static_branch_##name(struct jump_label_key *key) \
+static __always_inline bool static_branch_##name(struct static_key *key) \
{ \
return static_branch__##enabled(key); \
}
@@ -650,7 +650,7 @@
#undef SCHED_FEAT
-extern struct jump_label_key sched_feat_keys[__SCHED_FEAT_NR];
+extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
#define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
#else /* !(SCHED_DEBUG && HAVE_JUMP_LABEL) */
#define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index f1539de..d96ba22 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -25,7 +25,7 @@
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/sched.h>
-#include <linux/jump_label.h>
+#include <linux/static_key.h>
extern struct tracepoint * const __start___tracepoints_ptrs[];
extern struct tracepoint * const __stop___tracepoints_ptrs[];
@@ -256,9 +256,9 @@
{
WARN_ON(strcmp((*entry)->name, elem->name) != 0);
- if (elem->regfunc && !jump_label_enabled(&elem->key) && active)
+ if (elem->regfunc && !static_key_enabled(&elem->key) && active)
elem->regfunc();
- else if (elem->unregfunc && jump_label_enabled(&elem->key) && !active)
+ else if (elem->unregfunc && static_key_enabled(&elem->key) && !active)
elem->unregfunc();
/*
@@ -269,10 +269,10 @@
* is used.
*/
rcu_assign_pointer(elem->funcs, (*entry)->funcs);
- if (active && !jump_label_enabled(&elem->key))
- jump_label_inc(&elem->key);
- else if (!active && jump_label_enabled(&elem->key))
- jump_label_dec(&elem->key);
+ if (active && !static_key_enabled(&elem->key))
+ static_key_slow_inc(&elem->key);
+ else if (!active && static_key_enabled(&elem->key))
+ static_key_slow_dec(&elem->key);
}
/*
@@ -283,11 +283,11 @@
*/
static void disable_tracepoint(struct tracepoint *elem)
{
- if (elem->unregfunc && jump_label_enabled(&elem->key))
+ if (elem->unregfunc && static_key_enabled(&elem->key))
elem->unregfunc();
- if (jump_label_enabled(&elem->key))
- jump_label_dec(&elem->key);
+ if (static_key_enabled(&elem->key))
+ static_key_slow_dec(&elem->key);
rcu_assign_pointer(elem->funcs, NULL);
}