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, 4 insertions, 4 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c6414fc669d..423547ada38a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1399,20 +1399,20 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 #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)