perf/core: Set event's default ::overflow_handler()

Set a default event->overflow_handler in perf_event_alloc() so don't
need to check event->overflow_handler in __perf_event_overflow().
Following commits can give a different default overflow_handler.

Initial idea comes from Peter:

  http://lkml.kernel.org/r/20130708121557.GA17211@twins.programming.kicks-ass.net

Since the default value of event->overflow_handler is not NULL, existing
'if (!overflow_handler)' checks need to be changed.

is_default_overflow_handler() is introduced for this.

No extra performance overhead is introduced into the hot path because in the
original code we still need to read this handler from memory. A conditional
branch is avoided so actually we remove some instructions.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <pi3orama@163.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/1459147292-239310-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Chatur27 <jasonbright2709@gmail.com>

4 files changed, 24 insertions, 25 deletions

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 78c6be1b2714..89fd86301242 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -631,7 +631,7 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
 	info->address &= ~alignment_mask;
 	info->ctrl.len <<= offset;
 
-	if (!bp->overflow_handler) {
+	if (is_default_overflow_handler(bp)) {
 		/*
 		 * Mismatch breakpoints are required for single-stepping
 		 * breakpoints.
@@ -688,12 +688,6 @@ static void disable_single_step(struct perf_event *bp)
 	arch_install_hw_breakpoint(bp);
 }
 
-static int watchpoint_fault_on_uaccess(struct pt_regs *regs,
-				       struct arch_hw_breakpoint *info)
-{
-	return !user_mode(regs) && info->ctrl.privilege == ARM_BREAKPOINT_USER;
-}
-
 static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 			       struct pt_regs *regs)
 {
@@ -760,20 +754,17 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 		 * can't help us with this.
 		 */
 		if (watchpoint_fault_on_uaccess(regs, info))
-			goto step;
+			enable_single_step(wp, instruction_pointer(regs));
 
 		perf_bp_event(wp, regs);
 
 		/*
-		 * Defer stepping to the overflow handler if one is installed.
-		 * Otherwise, insert a temporary mismatch breakpoint so that
-		 * we can single-step over the watchpoint trigger.
+		 * If no overflow handler is present, insert a temporary
+		 * mismatch breakpoint so we can single-step over the
+		 * watchpoint trigger.
 		 */
-		if (wp->overflow_handler)
-			goto unlock;
-
-step:
-		enable_single_step(wp, instruction_pointer(regs));
+		if (is_default_overflow_handler(wp))
+			enable_single_step(wp, instruction_pointer(regs));
 unlock:
 		rcu_read_unlock();
 	}
@@ -1163,4 +1154,4 @@ int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 					unsigned long val, void *data)
 {
 	return NOTIFY_DONE;
-}
+}
\ No newline at end of file
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index bef4b659d816..3530541b3f5b 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -662,7 +662,7 @@ static int breakpoint_handler(unsigned long unused, unsigned int esr,
 		perf_bp_event(bp, regs);
 
 		/* Do we need to handle the stepping? */
-		if (!bp->overflow_handler)
+		if (is_default_overflow_handler(bp))
 			step = 1;
 unlock:
 		rcu_read_unlock();
@@ -788,7 +788,7 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr,
 		perf_bp_event(wp, regs);
 
 		/* Do we need to handle the stepping? */
-		if (!wp->overflow_handler)
+		if (is_default_overflow_handler(wp))
 			step = 1;
 	}
 	if (min_dist > 0 && min_dist != -1) {
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 8e50962b984b..f29f84898698 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -863,6 +863,12 @@ extern void perf_event_output(struct perf_event *event,
 				struct perf_sample_data *data,
 				struct pt_regs *regs);
 
+static inline bool
+is_default_overflow_handler(struct perf_event *event)
+{
+	return (event->overflow_handler == perf_event_output);
+}
+
 extern void
 perf_event_header__init_id(struct perf_event_header *header,
 			   struct perf_sample_data *data,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index befba6489d5e..658f21d9b180 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6700,10 +6700,7 @@ static int __perf_event_overflow(struct perf_event *event,
 		irq_work_queue(&event->pending);
 	}
 
-	if (event->overflow_handler)
-		event->overflow_handler(event, data, regs);
-	else
-		perf_event_output(event, data, regs);
+	event->overflow_handler(event, data, regs);
 
 	if (*perf_event_fasync(event) && event->pending_kill) {
 		event->pending_wakeup = 1;
@@ -8209,8 +8206,13 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 		context = parent_event->overflow_handler_context;
 	}
 
-	event->overflow_handler	= overflow_handler;
-	event->overflow_handler_context = context;
+	if (overflow_handler) {
+		event->overflow_handler	= overflow_handler;
+		event->overflow_handler_context = context;
+	} else {
+		event->overflow_handler = perf_event_output;
+		event->overflow_handler_context = NULL;
+	}
 
 	perf_event__state_init(event);