tracing: Add additional marks to signal very large time deltas

Currently, function graph tracer prints "!" or "+" just before
function execution time to signal a function overhead, depending
on the time. And some tracers tracing latency also print "!" or
"+" just after time to signal overhead, depending on the interval
between events. Even it is usually enough to do that, we sometimes
need to signal for bigger execution time than 100 micro seconds.

For example, I used function graph tracer to detect if there is
any case that exit_mm() takes too much time. I did following steps
in /sys/kernel/debug/tracing. It was easier to detect very large
excution time with patched kernel than with original kernel.

$ echo exit_mm > set_graph_function
$ echo function_graph > current_tracer
$ echo > trace
$ cat trace_pipe > $LOGFILE
 ... (do something and terminate logging)
$ grep "\\$" $LOGFILE
 3) $ 22082032 us |                      } /* kernel_map_pages */
 3) $ 22082040 us |                    } /* free_pages_prepare */
 3) $ 22082113 us |                  } /* free_hot_cold_page */
 3) $ 22083455 us |                } /* free_hot_cold_page_list */
 3) $ 22083895 us |              } /* release_pages */
 3) $ 22177873 us |            } /* free_pages_and_swap_cache */
 3) $ 22178929 us |          } /* unmap_single_vma */
 3) $ 22198885 us |        } /* unmap_vmas */
 3) $ 22206949 us |      } /* exit_mmap */
 3) $ 22207659 us |    } /* mmput */
 3) $ 22207793 us |  } /* exit_mm */

And then, it was easy to find out that a schedule-out occured by
sub_preempt_count() within kernel_map_pages().

To detect very large function exection time caused by either problematic
function implementation or scheduling issues, this patch can be useful.

Link: http://lkml.kernel.org/r/1416789259-24038-1-git-send-email-byungchul.park@lge.com

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 3 insertions, 20 deletions

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 100288d10e1f..6c2ab955018c 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -730,8 +730,6 @@ static void
 print_graph_duration(unsigned long long duration, struct trace_seq *s,
                      u32 flags)
 {
-        bool duration_printed = false;
-
         if (!(flags & TRACE_GRAPH_PRINT_DURATION) ||
             !(trace_flags & TRACE_ITER_CONTEXT_INFO))
                 return;
@@ -750,24 +748,9 @@ print_graph_duration(unsigned long long duration, struct trace_seq *s,
         }
 
         /* Signal a overhead of time execution to the output */
-        if (flags & TRACE_GRAPH_PRINT_OVERHEAD) {
-                /* Duration exceeded 100 usecs */
-                if (duration > 100000ULL) {
-                        trace_seq_puts(s, "! ");
-                        duration_printed = true;
-
-                /* Duration exceeded 10 usecs */
-                } else if (duration > 10000ULL) {
-                        trace_seq_puts(s, "+ ");
-                        duration_printed = true;
-                }
-        }
-
-        /*
-         * If we did not exceed the duration tresholds or we dont want
-         * to print out the overhead. Either way we need to fill out the space.
-         */
-        if (!duration_printed)
+        if (flags & TRACE_GRAPH_PRINT_OVERHEAD)
+                trace_seq_printf(s, "%c ", trace_find_mark(duration));
+        else
                 trace_seq_puts(s, "  ");
 
         trace_print_graph_duration(duration, s);