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, 9 insertions, 9 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5255c9d2e053..112c6824476b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -162,13 +162,13 @@ static int sched_feat_show(struct seq_file *m, void *v)
 
 #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 @@ struct jump_label_key sched_feat_keys[__SCHED_FEAT_NR] = {
 
 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 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
 	delta -= irq_delta;
 #endif
 #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
-	if (static_branch((&paravirt_steal_rq_enabled))) {
+	if (static_key_false((&paravirt_steal_rq_enabled))) {
 		u64 st;
 
 		steal = paravirt_steal_clock(cpu_of(rq));
@@ -2756,7 +2756,7 @@ void account_idle_time(cputime_t cputime)
 static __always_inline bool steal_account_process_tick(void)
 {
 #ifdef CONFIG_PARAVIRT
-	if (static_branch(&paravirt_steal_enabled)) {
+	if (static_key_false(&paravirt_steal_enabled)) {
 		u64 steal, st = 0;
 
 		steal = paravirt_steal_clock(smp_processor_id());