[PATCH] profiling: add tick tracepoint

[Frank Ch. Eigler]

Commit ba6fdda4 removed the timer_hook mechanism for modules to listen
to profiling timer ticks (without having to set up more complicated
perf mechanisms).  To reduce the impact on out-of-tree users such as
systemtap, a TRACE_EVENT-flavoured tracepoint is added in its place,
invoked right beside profile_tick() in kernel/time/tick-*.c.
Tested with perf and systemtap.

Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Frank Ch. Eigler <fche@xxxxxxxxxx>
---
 include/trace/events/timer.h | 20 ++++++++++++++++++++
 kernel/time/tick-common.c    |  2 ++
 kernel/time/tick-sched.c     |  2 ++
 3 files changed, 24 insertions(+)

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index 425bcfe..ec4c2d0 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -323,6 +323,26 @@ TRACE_EVENT(itimer_expire,
 		  (int) __entry->pid, (unsigned long long)__entry->now)
 );
 
+
+struct pt_regs;
+
+/**
+ * tick - called when the profiling timer ticks
+ * @regs:	pointer to struct pt_regs*
+ */
+TRACE_EVENT(tick,
+	TP_PROTO(struct pt_regs *regs),
+	TP_ARGS(regs),
+	TP_STRUCT__entry(
+		__field( struct pt_regs*,	regs	)
+	),
+	TP_fast_assign(
+		__entry->regs	= regs;
+	),
+	TP_printk("ip=%p", (void *) instruction_pointer(__entry->regs))
+);
+
+
 #endif /*  _TRACE_TIMER_H */
 
 /* This part must be outside protection */
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index b1600a6..5f4227f 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -18,6 +18,7 @@
 #include <linux/percpu.h>
 #include <linux/profile.h>
 #include <linux/sched.h>
+#include <trace/events/timer.h>
 
 #include <asm/irq_regs.h>
 
@@ -74,6 +75,7 @@ static void tick_periodic(int cpu)
 
 	update_process_times(user_mode(get_irq_regs()));
 	profile_tick(CPU_PROFILING);
+	trace_tick(get_irq_regs());
 }
 
 /*
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index a19a399..447be56 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -21,6 +21,7 @@
 #include <linux/sched.h>
 #include <linux/module.h>
 #include <linux/irq_work.h>
+#include <trace/events/timer.h>
 
 #include <asm/irq_regs.h>
 
@@ -140,6 +141,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
 #endif
 	update_process_times(user_mode(regs));
 	profile_tick(CPU_PROFILING);
+	trace_tick(get_irq_regs());
 }
 
 /*
-- 
1.8.2

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