tracing/function-graph-tracer: Output arrows signal on hardirq call/return

Impact: make more obvious the hardirq calls in the output

When a hardirq is triggered inside the codeflow on output, we have
now two arrows that indicate the entry and return of the hardirq.

 0)               |          bit_waitqueue() {
 0)   0.880 us    |            __phys_addr();
 0)   2.699 us    |          }
 0)               |          __wake_up_bit() {
 0)   ==========> |          smp_apic_timer_interrupt() {
 0)   0.797 us    |            native_apic_mem_write();
 0)   0.715 us    |            exit_idle();
 0)               |            irq_enter() {
 0)   0.722 us    |              idle_cpu();
 0)   5.519 us    |            }
 0)               |            hrtimer_interrupt() {
 0)               |              ktime_get() {
 0)               |                ktime_get_ts() {
 0)   0.805 us    |                  getnstimeofday();

 [...]

 0) ! 108.528 us  |            }
 0)               |            irq_exit() {
 0)               |              do_softirq() {
 0)               |                __do_softirq() {
 0)   0.895 us    |                  __local_bh_disable();
 0)               |                  run_timer_softirq() {
 0)   0.827 us    |                    hrtimer_run_pending();
 0)   1.226 us    |                    _spin_lock_irq();
 0)               |                    _spin_unlock_irq() {
 0)   6.550 us    |                  }
 0)   0.924 us    |                  _local_bh_enable();
 0) + 12.129 us   |                }
 0) + 13.911 us   |              }
 0)   0.707 us    |              idle_cpu();
 0) + 17.009 us   |            }
 0) ! 137.419 us  |          }
 0)   <========== |
 0)   1.045 us    |          }
 0) ! 148.908 us  |        }
 0) ! 151.022 us  |      }
 0) ! 153.022 us  |    }
 0)   0.963 us    |    journal_mark_dirty();
 0)   0.925 us    |    __brelse();
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_functions_graph.c

@@ -231,6 +231,49 @@ trace_branch_is_leaf(struct trace_iterator *iter,
 	return true;
 }
 
+static enum print_line_t
+print_graph_irq(struct trace_seq *s, unsigned long addr,
+				enum trace_type type, int cpu, pid_t pid)
+{
+	int ret;
+
+	if (addr < (unsigned long)__irqentry_text_start ||
+		addr >= (unsigned long)__irqentry_text_end)
+		return TRACE_TYPE_UNHANDLED;
+
+	if (type == TRACE_GRAPH_ENT) {
+		ret = trace_seq_printf(s, "==========> |  ");
+	} else {
+		/* Cpu */
+		if (tracer_flags.val & TRACE_GRAPH_PRINT_CPU) {
+			ret = print_graph_cpu(s, cpu);
+			if (ret == TRACE_TYPE_PARTIAL_LINE)
+				return TRACE_TYPE_PARTIAL_LINE;
+		}
+		/* Proc */
+		if (tracer_flags.val & TRACE_GRAPH_PRINT_PROC) {
+			ret = print_graph_proc(s, pid);
+			if (ret == TRACE_TYPE_PARTIAL_LINE)
+				return TRACE_TYPE_PARTIAL_LINE;
+
+			ret = trace_seq_printf(s, " | ");
+			if (!ret)
+				return TRACE_TYPE_PARTIAL_LINE;
+		}
+
+		/* No overhead */
+		if (tracer_flags.val & TRACE_GRAPH_PRINT_OVERHEAD) {
+			ret = trace_seq_printf(s, "  ");
+			if (!ret)
+				return TRACE_TYPE_PARTIAL_LINE;
+		}
+
+		ret = trace_seq_printf(s, "<========== |\n");
+	}
+	if (!ret)
+		return TRACE_TYPE_PARTIAL_LINE;
+	return TRACE_TYPE_HANDLED;
+}
 
 static enum print_line_t
 print_graph_duration(unsigned long long duration, struct trace_seq *s)
@@ -344,7 +387,7 @@ print_graph_entry_leaf(struct trace_iterator *iter,
 
 static enum print_line_t
 print_graph_entry_nested(struct ftrace_graph_ent_entry *entry,
-			struct trace_seq *s)
+			struct trace_seq *s, pid_t pid, int cpu)
 {
 	int i;
 	int ret;
@@ -357,8 +400,18 @@ print_graph_entry_nested(struct ftrace_graph_ent_entry *entry,
 			return TRACE_TYPE_PARTIAL_LINE;
 	}
 
+	/* Interrupt */
+	ret = print_graph_irq(s, call->func, TRACE_GRAPH_ENT, cpu, pid);
+	if (ret == TRACE_TYPE_UNHANDLED) {
 		/* No time */
 		ret = trace_seq_printf(s, "            |  ");
+		if (!ret)
+			return TRACE_TYPE_PARTIAL_LINE;
+	} else {
+		if (ret == TRACE_TYPE_PARTIAL_LINE)
+			return TRACE_TYPE_PARTIAL_LINE;
+	}
+
 
 	/* Function */
 	for (i = 0; i < call->depth * TRACE_GRAPH_INDENT; i++) {
@@ -410,7 +463,7 @@ print_graph_entry(struct ftrace_graph_ent_entry *field, struct trace_seq *s,
 	if (trace_branch_is_leaf(iter, field))
 		return print_graph_entry_leaf(iter, field, s);
 	else
-		return print_graph_entry_nested(field, s);
+		return print_graph_entry_nested(field, s, iter->ent->pid, cpu);
 
 }
 
@@ -474,6 +527,11 @@ print_graph_return(struct ftrace_graph_ret *trace, struct trace_seq *s,
 		if (!ret)
 			return TRACE_TYPE_PARTIAL_LINE;
 	}
+
+	ret = print_graph_irq(s, trace->func, TRACE_GRAPH_RET, cpu, ent->pid);
+	if (ret == TRACE_TYPE_PARTIAL_LINE)
+		return TRACE_TYPE_PARTIAL_LINE;
+
 	return TRACE_TYPE_HANDLED;
 }