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jump label: Introduce static_branch() interface

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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>
This commit is contained in:
Jason Baron 2011-03-16 17:29:47 -04:00 • committed by Steven Rostedt
parent ee5e51f51b
commit d430d3d7e6
15 changed files with 416 additions and 546 deletions
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91
include/linux/jump_label.h
View file

@ -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 jump_label_unlock(void);
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 int jump_label_text_reserved(void *start, void *end)
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