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/perf_event.h b/include/linux/perf_event.h
index 311b4dc..730b782 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -505,7 +505,7 @@
#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 @@
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 @@
{
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 @@
{
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);