Commit d430d3d7 authored by Jason Baron's avatar Jason Baron Committed by Steven Rostedt
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110316212947.GA8792@redhat.com>
Signed-off-by: default avatarJason Baron <jbaron@redhat.com>
Suggested-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Tested-by: default avatarDavid Daney <ddaney@caviumnetworks.com>
Acked-by: default avatarRalf Baechle <ralf@linux-mips.org>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Acked-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent ee5e51f5
......@@ -20,16 +20,18 @@
#define WORD_INSN ".word"
#endif
#define JUMP_LABEL(key, label) \
do { \
asm goto("1:\tnop\n\t" \
"nop\n\t" \
".pushsection __jump_table, \"a\"\n\t" \
WORD_INSN " 1b, %l[" #label "], %0\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:\tnop\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
WORD_INSN " 1b, %l[l_yes], %0\n\t"
".popsection\n\t"
: : "i" (key) : : l_yes);
return false;
l_yes:
return true;
}
#endif /* __KERNEL__ */
......
......@@ -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__ */
......
......@@ -4,7 +4,6 @@
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/stringify.h>
#include <linux/jump_label.h>
#include <asm/asm.h>
/*
......@@ -191,7 +190,7 @@ extern void *text_poke(void *addr, const void *opcode, size_t len);
extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
extern void text_poke_smp_batch(struct text_poke_param *params, int n);
#if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL)
#if defined(CONFIG_DYNAMIC_FTRACE) || defined(CONFIG_JUMP_LABEL)
#define IDEAL_NOP_SIZE_5 5
extern unsigned char ideal_nop5[IDEAL_NOP_SIZE_5];
extern void arch_init_ideal_nop5(void);
......
......@@ -5,20 +5,24 @@
#include <linux/types.h>
#include <asm/nops.h>
#include <asm/asm.h>
#define JUMP_LABEL_NOP_SIZE 5
# define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t"
# define JUMP_LABEL(key, label) \
do { \
asm goto("1:" \
JUMP_LABEL_INITIAL_NOP \
".pushsection __jump_table, \"aw\" \n\t"\
_ASM_PTR "1b, %l[" #label "], %c0 \n\t" \
".popsection \n\t" \
: : "i" (key) : : label); \
} while (0)
#define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t"
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
asm goto("1:"
JUMP_LABEL_INITIAL_NOP
".pushsection __jump_table, \"aw\" \n\t"
_ASM_PTR "1b, %l[l_yes], %c0 \n\t"
".popsection \n\t"
: : "i" (key) : : l_yes);
return false;
l_yes:
return true;
}
#endif /* __KERNEL__ */
......
......@@ -679,7 +679,7 @@ void __kprobes text_poke_smp_batch(struct text_poke_param *params, int n)
__stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
}
#if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL)
#if defined(CONFIG_DYNAMIC_FTRACE) || defined(CONFIG_JUMP_LABEL)
#ifdef CONFIG_X86_64
unsigned char ideal_nop5[5] = { 0x66, 0x66, 0x66, 0x66, 0x90 };
......
......@@ -24,6 +24,7 @@
#include <linux/bug.h>
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/jump_label.h>
#include <asm/system.h>
#include <asm/page.h>
......
......@@ -170,6 +170,10 @@
STRUCT_ALIGN(); \
*(__tracepoints) \
/* implement dynamic printk debug */ \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___jump_table) = .; \
*(__jump_table) \
VMLINUX_SYMBOL(__stop___jump_table) = .; \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___verbose) = .; \
*(__verbose) \
......@@ -228,8 +232,6 @@
\
BUG_TABLE \
\
JUMP_TABLE \
\
/* PCI quirks */ \
.pci_fixup : AT(ADDR(.pci_fixup) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start_pci_fixups_early) = .; \
......@@ -589,14 +591,6 @@
#define BUG_TABLE
#endif
#define JUMP_TABLE \
. = ALIGN(8); \
__jump_table : AT(ADDR(__jump_table) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start___jump_table) = .; \
*(__jump_table) \
VMLINUX_SYMBOL(__stop___jump_table) = .; \
}
#ifdef CONFIG_PM_TRACE
#define TRACEDATA \
. = ALIGN(4); \
......
#ifndef _DYNAMIC_DEBUG_H
#define _DYNAMIC_DEBUG_H
#include <linux/jump_label.h>
/* dynamic_printk_enabled, and dynamic_printk_enabled2 are bitmasks in which
* bit n is set to 1 if any modname hashes into the bucket n, 0 otherwise. They
* use independent hash functions, to reduce the chance of false positives.
......
#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);
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);
#define jump_label_enable(key) \
jump_label_update((unsigned long)key, JUMP_LABEL_ENABLE);
#else
#define jump_label_disable(key) \
jump_label_update((unsigned long)key, JUMP_LABEL_DISABLE);
#include <asm/atomic.h>
#else
#define JUMP_LABEL_INIT {ATOMIC_INIT(0)}
#define JUMP_LABEL(key, label) \
do { \
if (unlikely(*key)) \
goto label; \
} while (0)
struct jump_label_key {
atomic_t enabled;
};
#define jump_label_enable(cond_var) \
do { \
*(cond_var) = 1; \
} while (0)
static __always_inline bool static_branch(struct jump_label_key *key)
{
if (unlikely(atomic_read(&key->enabled)))
return true;
return false;
}
#define jump_label_disable(cond_var) \
do { \
*(cond_var) = 0; \
} while (0)
static inline void jump_label_inc(struct jump_label_key *key)
{
atomic_inc(&key->enabled);
}
static inline int jump_label_apply_nops(struct module *mod)
static inline void jump_label_dec(struct jump_label_key *key)
{
return 0;
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
#ifndef _LINUX_JUMP_LABEL_REF_H
#define _LINUX_JUMP_LABEL_REF_H
#include <linux/jump_label.h>
#include <asm/atomic.h>
#ifdef HAVE_JUMP_LABEL
static inline void jump_label_inc(atomic_t *key)
{
if (atomic_add_return(1, key) == 1)
jump_label_enable(key);
}
static inline void jump_label_dec(atomic_t *key)
{
if (atomic_dec_and_test(key))
jump_label_disable(key);
}
#else /* !HAVE_JUMP_LABEL */
static inline void jump_label_inc(atomic_t *key)
{
atomic_inc(key);
}
static inline void jump_label_dec(atomic_t *key)
{
atomic_dec(key);
}
#undef JUMP_LABEL
#define JUMP_LABEL(key, label) \
do { \
if (unlikely(__builtin_choose_expr( \
__builtin_types_compatible_p(typeof(key), atomic_t *), \
atomic_read((atomic_t *)(key)), *(key)))) \
goto label; \
} while (0)
#endif /* HAVE_JUMP_LABEL */
#endif /* _LINUX_JUMP_LABEL_REF_H */
......@@ -505,7 +505,7 @@ struct perf_guest_info_callbacks {
#include <linux/ftrace.h>
#include <linux/cpu.h>
#include <linux/irq_work.h>
#include <linux/jump_label_ref.h>
#include <linux/jump_label.h>
#include <asm/atomic.h>
#include <asm/local.h>
......@@ -1034,7 +1034,7 @@ static inline int is_software_event(struct perf_event *event)
return event->pmu->task_ctx_nr == perf_sw_context;
}
extern atomic_t perf_swevent_enabled[PERF_COUNT_SW_MAX];
extern struct jump_label_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
extern void __perf_sw_event(u32, u64, int, struct pt_regs *, u64);
......@@ -1063,22 +1063,21 @@ perf_sw_event(u32 event_id, u64 nr, int nmi, struct pt_regs *regs, u64 addr)
{
struct pt_regs hot_regs;
JUMP_LABEL(&perf_swevent_enabled[event_id], have_event);
return;
have_event:
if (!regs) {
perf_fetch_caller_regs(&hot_regs);
regs = &hot_regs;
if (static_branch(&perf_swevent_enabled[event_id])) {
if (!regs) {
perf_fetch_caller_regs(&hot_regs);
regs = &hot_regs;
}
__perf_sw_event(event_id, nr, nmi, regs, addr);
}
__perf_sw_event(event_id, nr, nmi, regs, addr);
}
extern atomic_t perf_sched_events;
extern struct jump_label_key perf_sched_events;
static inline void perf_event_task_sched_in(struct task_struct *task)
{
COND_STMT(&perf_sched_events, __perf_event_task_sched_in(task));
if (static_branch(&perf_sched_events))
__perf_event_task_sched_in(task);
}
static inline
......@@ -1086,7 +1085,8 @@ void perf_event_task_sched_out(struct task_struct *task, struct task_struct *nex
{
perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);
COND_STMT(&perf_sched_events, __perf_event_task_sched_out(task, next));
if (static_branch(&perf_sched_events))
__perf_event_task_sched_out(task, next);
}
extern void perf_event_mmap(struct vm_area_struct *vma);
......
......@@ -29,7 +29,7 @@ struct tracepoint_func {
struct tracepoint {
const char *name; /* Tracepoint name */
int state; /* State. */
struct jump_label_key key;
void (*regfunc)(void);
void (*unregfunc)(void);
struct tracepoint_func __rcu *funcs;
......@@ -146,9 +146,7 @@ void tracepoint_update_probe_range(struct tracepoint * const *begin,
extern struct tracepoint __tracepoint_##name; \
static inline void trace_##name(proto) \
{ \
JUMP_LABEL(&__tracepoint_##name.state, do_trace); \
return; \
do_trace: \
if (static_branch(&__tracepoint_##name.key)) \
__DO_TRACE(&__tracepoint_##name, \
TP_PROTO(data_proto), \
TP_ARGS(data_args), \
......@@ -176,14 +174,14 @@ do_trace: \
* structures, so we create an array of pointers that will be used for iteration
* on the tracepoints.
*/
#define DEFINE_TRACE_FN(name, reg, unreg) \
static const char __tpstrtab_##name[] \
__attribute__((section("__tracepoints_strings"))) = #name; \
struct tracepoint __tracepoint_##name \
__attribute__((section("__tracepoints"))) = \
{ __tpstrtab_##name, 0, reg, unreg, NULL }; \
static struct tracepoint * const __tracepoint_ptr_##name __used \
__attribute__((section("__tracepoints_ptrs"))) = \
#define DEFINE_TRACE_FN(name, reg, unreg) \
static const char __tpstrtab_##name[] \
__attribute__((section("__tracepoints_strings"))) = #name; \
struct tracepoint __tracepoint_##name \
__attribute__((section("__tracepoints"))) = \
{ __tpstrtab_##name, JUMP_LABEL_INIT, reg, unreg, NULL };\
static struct tracepoint * const __tracepoint_ptr_##name __used \
__attribute__((section("__tracepoints_ptrs"))) = \
&__tracepoint_##name;
#define DEFINE_TRACE(name) \
......
......@@ -2,43 +2,23 @@
* jump label support
*
* Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
* Copyright (C) 2011 Peter Zijlstra <pzijlstr@redhat.com>
*
*/
#include <linux/jump_label.h>
#include <linux/memory.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/jhash.h>
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/err.h>
#include <linux/jump_label.h>
#ifdef HAVE_JUMP_LABEL
#define JUMP_LABEL_HASH_BITS 6
#define JUMP_LABEL_TABLE_SIZE (1 << JUMP_LABEL_HASH_BITS)
static struct hlist_head jump_label_table[JUMP_LABEL_TABLE_SIZE];
/* mutex to protect coming/going of the the jump_label table */
static DEFINE_MUTEX(jump_label_mutex);
struct jump_label_entry {
struct hlist_node hlist;
struct jump_entry *table;
int nr_entries;
/* hang modules off here */
struct hlist_head modules;
unsigned long key;
};
struct jump_label_module_entry {
struct hlist_node hlist;
struct jump_entry *table;
int nr_entries;
struct module *mod;
};
void jump_label_lock(void)
{
mutex_lock(&jump_label_mutex);
......@@ -49,6 +29,11 @@ void jump_label_unlock(void)
mutex_unlock(&jump_label_mutex);
}
bool jump_label_enabled(struct jump_label_key *key)
{
return !!atomic_read(&key->enabled);
}
static int jump_label_cmp(const void *a, const void *b)
{
const struct jump_entry *jea = a;
......@@ -64,7 +49,7 @@ static int jump_label_cmp(const void *a, const void *b)
}
static void
sort_jump_label_entries(struct jump_entry *start, struct jump_entry *stop)
jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
{
unsigned long size;
......@@ -73,118 +58,25 @@ sort_jump_label_entries(struct jump_entry *start, struct jump_entry *stop)
sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
}
static struct jump_label_entry *get_jump_label_entry(jump_label_t key)
{
struct hlist_head *head;
struct hlist_node *node;
struct jump_label_entry *e;
u32 hash = jhash((void *)&key, sizeof(jump_label_t), 0);
head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
hlist_for_each_entry(e, node, head, hlist) {
if (key == e->key)
return e;
}
return NULL;
}
static void jump_label_update(struct jump_label_key *key, int enable);
static struct jump_label_entry *
add_jump_label_entry(jump_label_t key, int nr_entries, struct jump_entry *table)
void jump_label_inc(struct jump_label_key *key)
{
struct hlist_head *head;
struct jump_label_entry *e;
u32 hash;
e = get_jump_label_entry(key);
if (e)
return ERR_PTR(-EEXIST);
e = kmalloc(sizeof(struct jump_label_entry), GFP_KERNEL);
if (!e)
return ERR_PTR(-ENOMEM);
hash = jhash((void *)&key, sizeof(jump_label_t), 0);
head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
e->key = key;
e->table = table;
e->nr_entries = nr_entries;
INIT_HLIST_HEAD(&(e->modules));
hlist_add_head(&e->hlist, head);
return e;
}
if (atomic_inc_not_zero(&key->enabled))
return;
static int
build_jump_label_hashtable(struct jump_entry *start, struct jump_entry *stop)
{
struct jump_entry *iter, *iter_begin;
struct jump_label_entry *entry;
int count;
sort_jump_label_entries(start, stop);
iter = start;
while (iter < stop) {
entry = get_jump_label_entry(iter->key);
if (!entry) {
iter_begin = iter;
count = 0;
while ((iter < stop) &&
(iter->key == iter_begin->key)) {
iter++;
count++;
}
entry = add_jump_label_entry(iter_begin->key,
count, iter_begin);
if (IS_ERR(entry))
return PTR_ERR(entry);
} else {
WARN_ONCE(1, KERN_ERR "build_jump_hashtable: unexpected entry!\n");
return -1;
}
}
return 0;
jump_label_lock();
if (atomic_add_return(1, &key->enabled) == 1)
jump_label_update(key, JUMP_LABEL_ENABLE);
jump_label_unlock();
}
/***
* jump_label_update - update jump label text
* @key - key value associated with a a jump label
* @type - enum set to JUMP_LABEL_ENABLE or JUMP_LABEL_DISABLE
*
* Will enable/disable the jump for jump label @key, depending on the
* value of @type.
*
*/
void jump_label_update(unsigned long key, enum jump_label_type type)
void jump_label_dec(struct jump_label_key *key)
{
struct jump_entry *iter;
struct jump_label_entry *entry;
struct hlist_node *module_node;
struct jump_label_module_entry *e_module;
int count;
if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
return;
jump_label_lock();