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/arch/x86/kvm/mmu_audit.c b/arch/x86/kvm/mmu_audit.c
index fe15dcc07a6b..ea7b4fd34676 100644
--- a/arch/x86/kvm/mmu_audit.c
+++ b/arch/x86/kvm/mmu_audit.c
@@ -234,7 +234,7 @@ static void audit_vcpu_spte(struct kvm_vcpu *vcpu)
 }
 
 static bool mmu_audit;
-static struct jump_label_key mmu_audit_key;
+static struct static_key mmu_audit_key;
 
 static void __kvm_mmu_audit(struct kvm_vcpu *vcpu, int point)
 {
@@ -250,7 +250,7 @@ static void __kvm_mmu_audit(struct kvm_vcpu *vcpu, int point)
 
 static inline void kvm_mmu_audit(struct kvm_vcpu *vcpu, int point)
 {
-        if (static_branch((&mmu_audit_key)))
+        if (static_key_false((&mmu_audit_key)))
                 __kvm_mmu_audit(vcpu, point);
 }
 
@@ -259,7 +259,7 @@ static void mmu_audit_enable(void)
         if (mmu_audit)
                 return;
 
-        jump_label_inc(&mmu_audit_key);
+        static_key_slow_inc(&mmu_audit_key);
         mmu_audit = true;
 }
 
@@ -268,7 +268,7 @@ static void mmu_audit_disable(void)
         if (!mmu_audit)
                 return;
 
-        jump_label_dec(&mmu_audit_key);
+        static_key_slow_dec(&mmu_audit_key);
         mmu_audit = false;
 }