jump label: Introduce static_branch() interface

Introduce:

static __always_inline bool static_branch(struct jump_label_key *key);

instead of the old JUMP_LABEL(key, label) macro.

In this way, jump labels become really easy to use:

Define:

        struct jump_label_key jump_key;

Can be used as:

        if (static_branch(&jump_key))
                do unlikely code

enable/disale via:

        jump_label_inc(&jump_key);
        jump_label_dec(&jump_key);

that's it!

For the jump labels disabled case, the static_branch() becomes an
atomic_read(), and jump_label_inc()/dec() are simply atomic_inc(),
atomic_dec() operations. We show testing results for this change below.

Thanks to H. Peter Anvin for suggesting the 'static_branch()' construct.

Since we now require a 'struct jump_label_key *key', we can store a pointer into
the jump table addresses. In this way, we can enable/disable jump labels, in
basically constant time. This change allows us to completely remove the previous
hashtable scheme. Thanks to Peter Zijlstra for this re-write.

Testing:

I ran a series of 'tbench 20' runs 5 times (with reboots) for 3
configurations, where tracepoints were disabled.

jump label configured in
avg: 815.6

jump label *not* configured in (using atomic reads)
avg: 800.1

jump label *not* configured in (regular reads)
avg: 803.4

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110316212947.GA8792@redhat.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Suggested-by: H. Peter Anvin <hpa@linux.intel.com>
Tested-by: David Daney <ddaney@caviumnetworks.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 14 insertions, 11 deletions

diff --git a/arch/sparc/include/asm/jump_label.h b/arch/sparc/include/asm/jump_label.h
index 427d4684e0d2..fc73a82366f8 100644
--- a/arch/sparc/include/asm/jump_label.h
+++ b/arch/sparc/include/asm/jump_label.h
@@ -7,17 +7,20 @@
 
 #define JUMP_LABEL_NOP_SIZE 4
 
-#define JUMP_LABEL(key, label)                                  \
-        do {                                                    \
-                asm goto("1:\n\t"                               \
-                         "nop\n\t"                              \
-                         "nop\n\t"                              \
-                         ".pushsection __jump_table,  \"a\"\n\t"\
-                         ".align 4\n\t"                         \
-                         ".word 1b, %l[" #label "], %c0\n\t"    \
-                         ".popsection \n\t"                     \
-                         : :  "i" (key) :  : label);\
-        } while (0)
+static __always_inline bool arch_static_branch(struct jump_label_key *key)
+{
+                asm goto("1:\n\t"
+                         "nop\n\t"
+                         "nop\n\t"
+                         ".pushsection __jump_table,  \"aw\"\n\t"
+                         ".align 4\n\t"
+                         ".word 1b, %l[l_yes], %c0\n\t"
+                         ".popsection \n\t"
+                         : :  "i" (key) : : l_yes);
+        return false;
+l_yes:
+        return true;
+}
 
 #endif /* __KERNEL__ */