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>

1 files changed, 7 insertions, 7 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 98c0c2623db8..b4cd6d8ea150 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -611,7 +611,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
  * 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 @@ enum {
 #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 @@ static __always_inline bool static_branch_##name(struct jump_label_key *key) \
 
 #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))