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/kernel/jump_label.c b/kernel/jump_label.c
index 3b79bd9..74d1c09 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -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 @@
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 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(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
}
-static struct jump_label_entry *get_jump_label_entry(jump_label_t key)
+static void jump_label_update(struct jump_label_key *key, int enable);
+
+void jump_label_inc(struct jump_label_key *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 struct jump_label_entry *
-add_jump_label_entry(jump_label_t key, int nr_entries, struct jump_entry *table)
-{
- 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;
-}
-
-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_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)
-{
- 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_inc_not_zero(&key->enabled))
+ return;
jump_label_lock();
- entry = get_jump_label_entry((jump_label_t)key);
- if (entry) {
- count = entry->nr_entries;
- iter = entry->table;
- while (count--) {
- if (kernel_text_address(iter->code))
- arch_jump_label_transform(iter, type);
- iter++;
- }
- /* eanble/disable jump labels in modules */
- hlist_for_each_entry(e_module, module_node, &(entry->modules),
- hlist) {
- count = e_module->nr_entries;
- iter = e_module->table;
- while (count--) {
- if (iter->key &&
- kernel_text_address(iter->code))
- arch_jump_label_transform(iter, type);
- iter++;
- }
- }
- }
+ if (atomic_add_return(1, &key->enabled) == 1)
+ jump_label_update(key, JUMP_LABEL_ENABLE);
+ jump_label_unlock();
+}
+
+void jump_label_dec(struct jump_label_key *key)
+{
+ if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
+ return;
+
+ jump_label_update(key, JUMP_LABEL_DISABLE);
jump_label_unlock();
}
@@ -197,41 +89,254 @@
return 0;
}
-#ifdef CONFIG_MODULES
-
-static int module_conflict(void *start, void *end)
+static int __jump_label_text_reserved(struct jump_entry *iter_start,
+ struct jump_entry *iter_stop, void *start, void *end)
{
- struct hlist_head *head;
- struct hlist_node *node, *node_next, *module_node, *module_node_next;
- struct jump_label_entry *e;
- struct jump_label_module_entry *e_module;
struct jump_entry *iter;
- int i, count;
- int conflict = 0;
- for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
- head = &jump_label_table[i];
- hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
- hlist_for_each_entry_safe(e_module, module_node,
- module_node_next,
- &(e->modules), hlist) {
- count = e_module->nr_entries;
- iter = e_module->table;
- while (count--) {
- if (addr_conflict(iter, start, end)) {
- conflict = 1;
- goto out;
- }
- iter++;
- }
- }
- }
+ iter = iter_start;
+ while (iter < iter_stop) {
+ if (addr_conflict(iter, start, end))
+ return 1;
+ iter++;
}
-out:
- return conflict;
+
+ return 0;
}
+static void __jump_label_update(struct jump_label_key *key,
+ struct jump_entry *entry, int enable)
+{
+ for (; entry->key == (jump_label_t)(unsigned long)key; entry++) {
+ /*
+ * entry->code set to 0 invalidates module init text sections
+ * kernel_text_address() verifies we are not in core kernel
+ * init code, see jump_label_invalidate_module_init().
+ */
+ if (entry->code && kernel_text_address(entry->code))
+ arch_jump_label_transform(entry, enable);
+ }
+}
+
+/*
+ * Not all archs need this.
+ */
+void __weak arch_jump_label_text_poke_early(jump_label_t addr)
+{
+}
+
+static __init int jump_label_init(void)
+{
+ struct jump_entry *iter_start = __start___jump_table;
+ struct jump_entry *iter_stop = __stop___jump_table;
+ struct jump_label_key *key = NULL;
+ struct jump_entry *iter;
+
+ jump_label_lock();
+ jump_label_sort_entries(iter_start, iter_stop);
+
+ for (iter = iter_start; iter < iter_stop; iter++) {
+ arch_jump_label_text_poke_early(iter->code);
+ if (iter->key == (jump_label_t)(unsigned long)key)
+ continue;
+
+ key = (struct jump_label_key *)(unsigned long)iter->key;
+ atomic_set(&key->enabled, 0);
+ key->entries = iter;
+#ifdef CONFIG_MODULES
+ key->next = NULL;
#endif
+ }
+ jump_label_unlock();
+
+ return 0;
+}
+early_initcall(jump_label_init);
+
+#ifdef CONFIG_MODULES
+
+struct jump_label_mod {
+ struct jump_label_mod *next;
+ struct jump_entry *entries;
+ struct module *mod;
+};
+
+static int __jump_label_mod_text_reserved(void *start, void *end)
+{
+ struct module *mod;
+
+ mod = __module_text_address((unsigned long)start);
+ if (!mod)
+ return 0;
+
+ WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
+
+ return __jump_label_text_reserved(mod->jump_entries,
+ mod->jump_entries + mod->num_jump_entries,
+ start, end);
+}
+
+static void __jump_label_mod_update(struct jump_label_key *key, int enable)
+{
+ struct jump_label_mod *mod = key->next;
+
+ while (mod) {
+ __jump_label_update(key, mod->entries, enable);
+ mod = mod->next;
+ }
+}
+
+/***
+ * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
+ * @mod: module to patch
+ *
+ * Allow for run-time selection of the optimal nops. Before the module
+ * loads patch these with arch_get_jump_label_nop(), which is specified by
+ * the arch specific jump label code.
+ */
+void jump_label_apply_nops(struct module *mod)
+{
+ struct jump_entry *iter_start = mod->jump_entries;
+ struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
+ struct jump_entry *iter;
+
+ /* if the module doesn't have jump label entries, just return */
+ if (iter_start == iter_stop)
+ return;
+
+ for (iter = iter_start; iter < iter_stop; iter++)
+ arch_jump_label_text_poke_early(iter->code);
+}
+
+static int jump_label_add_module(struct module *mod)
+{
+ struct jump_entry *iter_start = mod->jump_entries;
+ struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
+ struct jump_entry *iter;
+ struct jump_label_key *key = NULL;
+ struct jump_label_mod *jlm;
+
+ /* if the module doesn't have jump label entries, just return */
+ if (iter_start == iter_stop)
+ return 0;
+
+ jump_label_sort_entries(iter_start, iter_stop);
+
+ for (iter = iter_start; iter < iter_stop; iter++) {
+ if (iter->key == (jump_label_t)(unsigned long)key)
+ continue;
+
+ key = (struct jump_label_key *)(unsigned long)iter->key;
+
+ if (__module_address(iter->key) == mod) {
+ atomic_set(&key->enabled, 0);
+ key->entries = iter;
+ key->next = NULL;
+ continue;
+ }
+
+ jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
+ if (!jlm)
+ return -ENOMEM;
+
+ jlm->mod = mod;
+ jlm->entries = iter;
+ jlm->next = key->next;
+ key->next = jlm;
+
+ if (jump_label_enabled(key))
+ __jump_label_update(key, iter, JUMP_LABEL_ENABLE);
+ }
+
+ return 0;
+}
+
+static void jump_label_del_module(struct module *mod)
+{
+ struct jump_entry *iter_start = mod->jump_entries;
+ struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
+ struct jump_entry *iter;
+ struct jump_label_key *key = NULL;
+ struct jump_label_mod *jlm, **prev;
+
+ for (iter = iter_start; iter < iter_stop; iter++) {
+ if (iter->key == (jump_label_t)(unsigned long)key)
+ continue;
+
+ key = (struct jump_label_key *)(unsigned long)iter->key;
+
+ if (__module_address(iter->key) == mod)
+ continue;
+
+ prev = &key->next;
+ jlm = key->next;
+
+ while (jlm && jlm->mod != mod) {
+ prev = &jlm->next;
+ jlm = jlm->next;
+ }
+
+ if (jlm) {
+ *prev = jlm->next;
+ kfree(jlm);
+ }
+ }
+}
+
+static void jump_label_invalidate_module_init(struct module *mod)
+{
+ struct jump_entry *iter_start = mod->jump_entries;
+ struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
+ struct jump_entry *iter;
+
+ for (iter = iter_start; iter < iter_stop; iter++) {
+ if (within_module_init(iter->code, mod))
+ iter->code = 0;
+ }
+}
+
+static int
+jump_label_module_notify(struct notifier_block *self, unsigned long val,
+ void *data)
+{
+ struct module *mod = data;
+ int ret = 0;
+
+ switch (val) {
+ case MODULE_STATE_COMING:
+ jump_label_lock();
+ ret = jump_label_add_module(mod);
+ if (ret)
+ jump_label_del_module(mod);
+ jump_label_unlock();
+ break;
+ case MODULE_STATE_GOING:
+ jump_label_lock();
+ jump_label_del_module(mod);
+ jump_label_unlock();
+ break;
+ case MODULE_STATE_LIVE:
+ jump_label_lock();
+ jump_label_invalidate_module_init(mod);
+ jump_label_unlock();
+ break;
+ }
+
+ return notifier_from_errno(ret);
+}
+
+struct notifier_block jump_label_module_nb = {
+ .notifier_call = jump_label_module_notify,
+ .priority = 1, /* higher than tracepoints */
+};
+
+static __init int jump_label_init_module(void)
+{
+ return register_module_notifier(&jump_label_module_nb);
+}
+early_initcall(jump_label_init_module);
+
+#endif /* CONFIG_MODULES */
/***
* jump_label_text_reserved - check if addr range is reserved
@@ -248,237 +353,29 @@
*/
int jump_label_text_reserved(void *start, void *end)
{
- struct jump_entry *iter;
- struct jump_entry *iter_start = __start___jump_table;
- struct jump_entry *iter_stop = __start___jump_table;
- int conflict = 0;
+ int ret = __jump_label_text_reserved(__start___jump_table,
+ __stop___jump_table, start, end);
- iter = iter_start;
- while (iter < iter_stop) {
- if (addr_conflict(iter, start, end)) {
- conflict = 1;
- goto out;
- }
- iter++;
- }
+ if (ret)
+ return ret;
- /* now check modules */
#ifdef CONFIG_MODULES
- conflict = module_conflict(start, end);
+ ret = __jump_label_mod_text_reserved(start, end);
#endif
-out:
- return conflict;
-}
-
-/*
- * Not all archs need this.
- */
-void __weak arch_jump_label_text_poke_early(jump_label_t addr)
-{
-}
-
-static __init int init_jump_label(void)
-{
- int ret;
- struct jump_entry *iter_start = __start___jump_table;
- struct jump_entry *iter_stop = __stop___jump_table;
- struct jump_entry *iter;
-
- jump_label_lock();
- ret = build_jump_label_hashtable(__start___jump_table,
- __stop___jump_table);
- iter = iter_start;
- while (iter < iter_stop) {
- arch_jump_label_text_poke_early(iter->code);
- iter++;
- }
- jump_label_unlock();
return ret;
}
-early_initcall(init_jump_label);
+
+static void jump_label_update(struct jump_label_key *key, int enable)
+{
+ struct jump_entry *entry = key->entries;
+
+ /* if there are no users, entry can be NULL */
+ if (entry)
+ __jump_label_update(key, entry, enable);
#ifdef CONFIG_MODULES
-
-static struct jump_label_module_entry *
-add_jump_label_module_entry(struct jump_label_entry *entry,
- struct jump_entry *iter_begin,
- int count, struct module *mod)
-{
- struct jump_label_module_entry *e;
-
- e = kmalloc(sizeof(struct jump_label_module_entry), GFP_KERNEL);
- if (!e)
- return ERR_PTR(-ENOMEM);
- e->mod = mod;
- e->nr_entries = count;
- e->table = iter_begin;
- hlist_add_head(&e->hlist, &entry->modules);
- return e;
+ __jump_label_mod_update(key, enable);
+#endif
}
-static int add_jump_label_module(struct module *mod)
-{
- struct jump_entry *iter, *iter_begin;
- struct jump_label_entry *entry;
- struct jump_label_module_entry *module_entry;
- int count;
-
- /* if the module doesn't have jump label entries, just return */
- if (!mod->num_jump_entries)
- return 0;
-
- sort_jump_label_entries(mod->jump_entries,
- mod->jump_entries + mod->num_jump_entries);
- iter = mod->jump_entries;
- while (iter < mod->jump_entries + mod->num_jump_entries) {
- entry = get_jump_label_entry(iter->key);
- iter_begin = iter;
- count = 0;
- while ((iter < mod->jump_entries + mod->num_jump_entries) &&
- (iter->key == iter_begin->key)) {
- iter++;
- count++;
- }
- if (!entry) {
- entry = add_jump_label_entry(iter_begin->key, 0, NULL);
- if (IS_ERR(entry))
- return PTR_ERR(entry);
- }
- module_entry = add_jump_label_module_entry(entry, iter_begin,
- count, mod);
- if (IS_ERR(module_entry))
- return PTR_ERR(module_entry);
- }
- return 0;
-}
-
-static void remove_jump_label_module(struct module *mod)
-{
- struct hlist_head *head;
- struct hlist_node *node, *node_next, *module_node, *module_node_next;
- struct jump_label_entry *e;
- struct jump_label_module_entry *e_module;
- int i;
-
- /* if the module doesn't have jump label entries, just return */
- if (!mod->num_jump_entries)
- return;
-
- for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
- head = &jump_label_table[i];
- hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
- hlist_for_each_entry_safe(e_module, module_node,
- module_node_next,
- &(e->modules), hlist) {
- if (e_module->mod == mod) {
- hlist_del(&e_module->hlist);
- kfree(e_module);
- }
- }
- if (hlist_empty(&e->modules) && (e->nr_entries == 0)) {
- hlist_del(&e->hlist);
- kfree(e);
- }
- }
- }
-}
-
-static void remove_jump_label_module_init(struct module *mod)
-{
- struct hlist_head *head;
- struct hlist_node *node, *node_next, *module_node, *module_node_next;
- struct jump_label_entry *e;
- struct jump_label_module_entry *e_module;
- struct jump_entry *iter;
- int i, count;
-
- /* if the module doesn't have jump label entries, just return */
- if (!mod->num_jump_entries)
- return;
-
- for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
- head = &jump_label_table[i];
- hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
- hlist_for_each_entry_safe(e_module, module_node,
- module_node_next,
- &(e->modules), hlist) {
- if (e_module->mod != mod)
- continue;
- count = e_module->nr_entries;
- iter = e_module->table;
- while (count--) {
- if (within_module_init(iter->code, mod))
- iter->key = 0;
- iter++;
- }
- }
- }
- }
-}
-
-static int
-jump_label_module_notify(struct notifier_block *self, unsigned long val,
- void *data)
-{
- struct module *mod = data;
- int ret = 0;
-
- switch (val) {
- case MODULE_STATE_COMING:
- jump_label_lock();
- ret = add_jump_label_module(mod);
- if (ret)
- remove_jump_label_module(mod);
- jump_label_unlock();
- break;
- case MODULE_STATE_GOING:
- jump_label_lock();
- remove_jump_label_module(mod);
- jump_label_unlock();
- break;
- case MODULE_STATE_LIVE:
- jump_label_lock();
- remove_jump_label_module_init(mod);
- jump_label_unlock();
- break;
- }
- return ret;
-}
-
-/***
- * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
- * @mod: module to patch
- *
- * Allow for run-time selection of the optimal nops. Before the module
- * loads patch these with arch_get_jump_label_nop(), which is specified by
- * the arch specific jump label code.
- */
-void jump_label_apply_nops(struct module *mod)
-{
- struct jump_entry *iter;
-
- /* if the module doesn't have jump label entries, just return */
- if (!mod->num_jump_entries)
- return;
-
- iter = mod->jump_entries;
- while (iter < mod->jump_entries + mod->num_jump_entries) {
- arch_jump_label_text_poke_early(iter->code);
- iter++;
- }
-}
-
-struct notifier_block jump_label_module_nb = {
- .notifier_call = jump_label_module_notify,
- .priority = 0,
-};
-
-static __init int init_jump_label_module(void)
-{
- return register_module_notifier(&jump_label_module_nb);
-}
-early_initcall(init_jump_label_module);
-
-#endif /* CONFIG_MODULES */
-
#endif
