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/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 13009d1..8cdd1e2 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -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_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);
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 574dbc2..f217cee 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -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_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)
+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__ */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 4a23467..651454b 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -679,7 +679,7 @@
__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 };
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index ab23f1a..52f256f 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -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>