[PATCH v2 31/35] tracing: support lazy resched

[Ankur Arora]

trace_entry::flags is full, so reuse the TRACE_FLAG_IRQS_NOSUPPORT
bit for this. The flag is safe to reuse since it is only used in
old archs that don't support lockdep irq tracing.

Also, now that we have a variety of need-resched combinations, document
these in the tracing headers.

Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Originally-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
 include/linux/trace_events.h |  6 +++---
 kernel/trace/trace.c         | 28 ++++++++++++++++++----------
 kernel/trace/trace_output.c  | 16 ++++++++++++++--
 3 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 6f9bdfb09d1d..329002785b4d 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -184,7 +184,7 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status);
 
 enum trace_flag_type {
 	TRACE_FLAG_IRQS_OFF		= 0x01,
-	TRACE_FLAG_IRQS_NOSUPPORT	= 0x02,
+	TRACE_FLAG_NEED_RESCHED_LAZY    = 0x02,
 	TRACE_FLAG_NEED_RESCHED		= 0x04,
 	TRACE_FLAG_HARDIRQ		= 0x08,
 	TRACE_FLAG_SOFTIRQ		= 0x10,
@@ -211,11 +211,11 @@ static inline unsigned int tracing_gen_ctx(void)
 
 static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags)
 {
-	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
+	return tracing_gen_ctx_irq_test(0);
 }
 static inline unsigned int tracing_gen_ctx(void)
 {
-	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
+	return tracing_gen_ctx_irq_test(0);
 }
 #endif
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ed229527be05..7941e9ec979a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2513,6 +2513,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)
 
 	if (__tif_need_resched(RESCHED_NOW))
 		trace_flags |= TRACE_FLAG_NEED_RESCHED;
+	if (__tif_need_resched(RESCHED_LAZY))
+		trace_flags |= TRACE_FLAG_NEED_RESCHED_LAZY;
 	if (test_preempt_need_resched())
 		trace_flags |= TRACE_FLAG_PREEMPT_RESCHED;
 	return (trace_flags << 16) | (min_t(unsigned int, pc & 0xff, 0xf)) |
@@ -4096,17 +4098,23 @@ unsigned long trace_total_entries(struct trace_array *tr)
 	return entries;
 }
 
+#ifdef CONFIG_PREEMPT_AUTO
+#define NR_LEGEND "l: lazy, n: now, p: preempt, b: l|n, L: l|p, N: n|p, B: l|n|p"
+#else
+#define NR_LEGEND "n: now, p: preempt, N: n|p"
+#endif
+
 static void print_lat_help_header(struct seq_file *m)
 {
-	seq_puts(m, "#                    _------=> CPU#            \n"
-		    "#                   / _-----=> irqs-off/BH-disabled\n"
-		    "#                  | / _----=> need-resched    \n"
-		    "#                  || / _---=> hardirq/softirq \n"
-		    "#                  ||| / _--=> preempt-depth   \n"
-		    "#                  |||| / _-=> migrate-disable \n"
-		    "#                  ||||| /     delay           \n"
-		    "#  cmd     pid     |||||| time  |   caller     \n"
-		    "#     \\   /        ||||||  \\    |    /       \n");
+	seq_printf(m, "#                    _------=> CPU#            \n"
+		      "#                   / _-----=> irqs-off/BH-disabled\n"
+		      "#                  | / _----=> need-resched ( %s ) \n"
+		      "#                  || / _---=> hardirq/softirq \n"
+		      "#                  ||| / _--=> preempt-depth   \n"
+		      "#                  |||| / _-=> migrate-disable \n"
+		      "#                  ||||| /     delay           \n"
+		      "#  cmd     pid     |||||| time  |   caller     \n"
+		      "#     \\   /        ||||||  \\    |    /       \n", NR_LEGEND);
 }
 
 static void print_event_info(struct array_buffer *buf, struct seq_file *m)
@@ -4141,7 +4149,7 @@ static void print_func_help_header_irq(struct array_buffer *buf, struct seq_file
 	print_event_info(buf, m);
 
 	seq_printf(m, "#                            %.*s  _-----=> irqs-off/BH-disabled\n", prec, space);
-	seq_printf(m, "#                            %.*s / _----=> need-resched\n", prec, space);
+	seq_printf(m, "#                            %.*s / _----=> need-resched ( %s )\n", prec, space, NR_LEGEND);
 	seq_printf(m, "#                            %.*s| / _---=> hardirq/softirq\n", prec, space);
 	seq_printf(m, "#                            %.*s|| / _--=> preempt-depth\n", prec, space);
 	seq_printf(m, "#                            %.*s||| / _-=> migrate-disable\n", prec, space);
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d01083..4f58a196e14c 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -460,17 +460,29 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
 		(entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :
 		(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
 		bh_off ? 'b' :
-		(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
+		!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' :
 		'.';
 
-	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
+	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY |
 				TRACE_FLAG_PREEMPT_RESCHED)) {
+	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
+		need_resched = 'B';
+		break;
 	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
 		need_resched = 'N';
 		break;
+	case TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
+		need_resched = 'L';
+		break;
+	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY:
+		need_resched = 'b';
+		break;
 	case TRACE_FLAG_NEED_RESCHED:
 		need_resched = 'n';
 		break;
+	case TRACE_FLAG_NEED_RESCHED_LAZY:
+		need_resched = 'l';
+		break;
 	case TRACE_FLAG_PREEMPT_RESCHED:
 		need_resched = 'p';
 		break;
-- 
2.31.1