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>
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 7880f18..83e745f 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -1,20 +1,43 @@
#ifndef _LINUX_JUMP_LABEL_H
#define _LINUX_JUMP_LABEL_H
+#include <linux/types.h>
+#include <linux/compiler.h>
+
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
+
+struct jump_label_key {
+ atomic_t enabled;
+ struct jump_entry *entries;
+#ifdef CONFIG_MODULES
+ struct jump_label_mod *next;
+#endif
+};
+
# include <asm/jump_label.h>
# define HAVE_JUMP_LABEL
#endif
enum jump_label_type {
+ JUMP_LABEL_DISABLE = 0,
JUMP_LABEL_ENABLE,
- JUMP_LABEL_DISABLE
};
struct module;
#ifdef HAVE_JUMP_LABEL
+#ifdef CONFIG_MODULES
+#define JUMP_LABEL_INIT {{ 0 }, NULL, NULL}
+#else
+#define JUMP_LABEL_INIT {{ 0 }, NULL}
+#endif
+
+static __always_inline bool static_branch(struct jump_label_key *key)
+{
+ return arch_static_branch(key);
+}
+
extern struct jump_entry __start___jump_table[];
extern struct jump_entry __stop___jump_table[];
@@ -23,37 +46,37 @@
extern void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type);
extern void arch_jump_label_text_poke_early(jump_label_t addr);
-extern void jump_label_update(unsigned long key, enum jump_label_type type);
-extern void jump_label_apply_nops(struct module *mod);
extern int jump_label_text_reserved(void *start, void *end);
-
-#define jump_label_enable(key) \
- jump_label_update((unsigned long)key, JUMP_LABEL_ENABLE);
-
-#define jump_label_disable(key) \
- jump_label_update((unsigned long)key, JUMP_LABEL_DISABLE);
+extern void jump_label_inc(struct jump_label_key *key);
+extern void jump_label_dec(struct jump_label_key *key);
+extern bool jump_label_enabled(struct jump_label_key *key);
+extern void jump_label_apply_nops(struct module *mod);
#else
-#define JUMP_LABEL(key, label) \
-do { \
- if (unlikely(*key)) \
- goto label; \
-} while (0)
+#include <asm/atomic.h>
-#define jump_label_enable(cond_var) \
-do { \
- *(cond_var) = 1; \
-} while (0)
+#define JUMP_LABEL_INIT {ATOMIC_INIT(0)}
-#define jump_label_disable(cond_var) \
-do { \
- *(cond_var) = 0; \
-} while (0)
+struct jump_label_key {
+ atomic_t enabled;
+};
-static inline int jump_label_apply_nops(struct module *mod)
+static __always_inline bool static_branch(struct jump_label_key *key)
{
- return 0;
+ if (unlikely(atomic_read(&key->enabled)))
+ return true;
+ return false;
+}
+
+static inline void jump_label_inc(struct jump_label_key *key)
+{
+ atomic_inc(&key->enabled);
+}
+
+static inline void jump_label_dec(struct jump_label_key *key)
+{
+ atomic_dec(&key->enabled);
}
static inline int jump_label_text_reserved(void *start, void *end)
@@ -64,16 +87,16 @@
static inline void jump_label_lock(void) {}
static inline void jump_label_unlock(void) {}
-#endif
+static inline bool jump_label_enabled(struct jump_label_key *key)
+{
+ return !!atomic_read(&key->enabled);
+}
-#define COND_STMT(key, stmt) \
-do { \
- __label__ jl_enabled; \
- JUMP_LABEL(key, jl_enabled); \
- if (0) { \
-jl_enabled: \
- stmt; \
- } \
-} while (0)
+static inline int jump_label_apply_nops(struct module *mod)
+{
+ return 0;
+}
+
+#endif
#endif