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/include/linux/tracepoint.h b/include/linux/tracepoint.h
index fc36da97ff7..bd96ecd0e05 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -17,7 +17,7 @@
 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/rcupdate.h>
-#include <linux/jump_label.h>
+#include <linux/static_key.h>
 
 struct module;
 struct tracepoint;
@@ -29,7 +29,7 @@ struct tracepoint_func {
 
 struct tracepoint {
         const char *name;               /* Tracepoint name */
-        struct jump_label_key key;
+        struct static_key key;
         void (*regfunc)(void);
         void (*unregfunc)(void);
         struct tracepoint_func __rcu *funcs;
@@ -145,7 +145,7 @@ static inline void tracepoint_synchronize_unregister(void)
         extern struct tracepoint __tracepoint_##name;                   \
         static inline void trace_##name(proto)                          \
         {                                                               \
-                if (static_branch(&__tracepoint_##name.key))            \
+                if (static_key_false(&__tracepoint_##name.key))         \
                         __DO_TRACE(&__tracepoint_##name,                \
                                 TP_PROTO(data_proto),                   \
                                 TP_ARGS(data_args),                     \
@@ -188,7 +188,7 @@ static inline void tracepoint_synchronize_unregister(void)
         __attribute__((section("__tracepoints_strings"))) = #name;       \
         struct tracepoint __tracepoint_##name                            \
         __attribute__((section("__tracepoints"))) =                      \
-                { __tpstrtab_##name, JUMP_LABEL_INIT, reg, unreg, NULL };\
+                { __tpstrtab_##name, STATIC_KEY_INIT_FALSE, reg, unreg, NULL };\
         static struct tracepoint * const __tracepoint_ptr_##name __used  \
         __attribute__((section("__tracepoints_ptrs"))) =                 \
                 &__tracepoint_##name;