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authorIngo Molnar <mingo@elte.hu>2012-02-24 08:31:31 +0100
committerIngo Molnar <mingo@elte.hu>2012-02-24 10:05:59 +0100
commitc5905afb0ee6550b42c49213da1c22d67316c194 (patch)
tree253fdb322e6e5b257ffda3b9b66bce90a473a6f7 /kernel/jump_label.c
parent1cfa60dc7d7c7cc774a44eee47ff135a644a1f31 (diff)
downloadlinux-sh-c5905afb0ee6550b42c49213da1c22d67316c194.tar.gz
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>
Diffstat (limited to 'kernel/jump_label.c')
-rw-r--r--kernel/jump_label.c128
1 files changed, 74 insertions, 54 deletions
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 543782e7cdd2..bf9dcadbb53a 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 @@ void jump_label_unlock(void)
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 @@ jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
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 @@ static void __jump_label_dec(struct jump_label_key *key,
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 @@ void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry
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 void __jump_label_update(struct jump_label_key *key,
}
}
+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 @@ void __init jump_label_init(void)
#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 @@ static int __jump_label_mod_text_reserved(void *start, void *end)
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 @@ void jump_label_apply_nops(struct module *mod)
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 @@ static int jump_label_add_module(struct module *mod)
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 @@ static int jump_label_add_module(struct module *mod)
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)
- continue;
+ struct static_key *iterk;
- key = (struct jump_label_key *)(unsigned long)iter->key;
+ iterk = (struct static_key *)(unsigned long)iter->key;
+ if (iterk == key)
+ continue;
+ 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 @@ static void jump_label_del_module(struct module *mod)
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 @@ int jump_label_text_reserved(void *start, void *end)
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);