ftrace, sched: Add TRACE_FLAG_PREEMPT_RESCHED

Since the introduction of PREEMPT_NEED_RESCHED in:

  f27dde8 ("sched: Add NEED_RESCHED to the preempt_count")

we need to be able to look at both TIF_NEED_RESCHED and
PREEMPT_NEED_RESCHED to understand the full preemption behaviour.

Add it to the trace output.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Link: http://lkml.kernel.org/r/20131004152826.GP3081@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/trace/ftrace.txt

@@ -655,7 +655,11 @@ explains which is which.
 		  read the irq flags variable, an 'X' will always
 		  be printed here.
 
-  need-resched: 'N' task need_resched is set, '.' otherwise.
+  need-resched:
+	'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
+	'n' only TIF_NEED_RESCHED is set,
+	'p' only PREEMPT_NEED_RESCHED is set,
+	'.' otherwise.
 
   hardirq/softirq:
 	'H' - hard irq occurred inside a softirq.

kernel/trace/trace.c

@@ -1509,7 +1509,8 @@ tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
 #endif
 		((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) |
 		((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) |
-		(need_resched() ? TRACE_FLAG_NEED_RESCHED : 0);
+		(tif_need_resched() ? TRACE_FLAG_NEED_RESCHED : 0) |
+		(test_preempt_need_resched() ? TRACE_FLAG_PREEMPT_RESCHED : 0);
 }
 EXPORT_SYMBOL_GPL(tracing_generic_entry_update);
 

kernel/trace/trace.h

@@ -124,6 +124,7 @@ enum trace_flag_type {
 	TRACE_FLAG_NEED_RESCHED		= 0x04,
 	TRACE_FLAG_HARDIRQ		= 0x08,
 	TRACE_FLAG_SOFTIRQ		= 0x10,
+	TRACE_FLAG_PREEMPT_RESCHED	= 0x20,
 };
 
 #define TRACE_BUF_SIZE		1024

kernel/trace/trace_output.c

@@ -618,8 +618,23 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
 		(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
 		(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
 		'.';
-	need_resched =
-		(entry->flags & TRACE_FLAG_NEED_RESCHED) ? 'N' : '.';
+
+	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
+				TRACE_FLAG_PREEMPT_RESCHED)) {
+	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
+		need_resched = 'N';
+		break;
+	case TRACE_FLAG_NEED_RESCHED:
+		need_resched = 'n';
+		break;
+	case TRACE_FLAG_PREEMPT_RESCHED:
+		need_resched = 'p';
+		break;
+	default:
+		need_resched = '.';
+		break;
+	}
+
 	hardsoft_irq =
 		(hardirq && softirq) ? 'H' :
 		hardirq ? 'h' :