timers: Make flags output in the timer_start tracepoint useful

The timer flags in the timer_start trace event contain lots of useful
information, but the meaning is not clear in the trace output. Making tools
rely on the bit positions is bad as they might change over time.

Decode the flags in the print out. Tools can retrieve the bits and their
meaning from the trace format file.

Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1702101639290.4036@nanos

Requested-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/timer.h

@@ -66,6 +66,8 @@ struct timer_list {
 #define TIMER_ARRAYSHIFT	22
 #define TIMER_ARRAYMASK		0xFFC00000
 
+#define TIMER_TRACE_FLAGMASK	(TIMER_MIGRATING | TIMER_DEFERRABLE | TIMER_PINNED | TIMER_IRQSAFE)
+
 #define __TIMER_INITIALIZER(_function, _expires, _data, _flags) { \
 		.entry = { .next = TIMER_ENTRY_STATIC },	\
 		.function = (_function),			\

include/trace/events/timer.h

@@ -36,6 +36,13 @@ DEFINE_EVENT(timer_class, timer_init,
 	TP_ARGS(timer)
 );
 
+#define decode_timer_flags(flags)			\
+	__print_flags(flags, "|",			\
+		{  TIMER_MIGRATING,	"M" },		\
+		{  TIMER_DEFERRABLE,	"D" },		\
+		{  TIMER_PINNED,	"P" },		\
+		{  TIMER_IRQSAFE,	"I" })
+
 /**
  * timer_start - called when the timer is started
  * @timer:	pointer to struct timer_list
@@ -65,9 +72,12 @@ TRACE_EVENT(timer_start,
 		__entry->flags		= flags;
 	),
 
-	TP_printk("timer=%p function=%pf expires=%lu [timeout=%ld] flags=0x%08x",
+	TP_printk("timer=%p function=%pf expires=%lu [timeout=%ld] cpu=%u idx=%u flags=%s",
 		  __entry->timer, __entry->function, __entry->expires,
-		  (long)__entry->expires - __entry->now, __entry->flags)
+		  (long)__entry->expires - __entry->now,
+		  __entry->flags & TIMER_CPUMASK,
+		  __entry->flags >> TIMER_ARRAYSHIFT,
+		  decode_timer_flags(__entry->flags & TIMER_TRACE_FLAGMASK))
 );
 
 /**