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/tracepoint.h b/include/linux/tracepoint.h
index 97c84a5..d530a44 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -29,7 +29,7 @@
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 @@
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 @@
* 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) \