Markers show sudden variation in atomic events. They can be enabled by configuring TAU with 
-useropt=-DTAU_USE_EVENT_THRESHOLDS. By default, when an atomic events value changes by 10%, 
a marker context event is triggered with the value that caused this condition. To change the threshold to 
something other than 0.1 (or 10%) to say 0.5 (or 50%), you may configure using:
-useropt=-DTAU_USE_EVENT_THRESHOLDS#-DTAU_EVENT_THRESHOLD=0.5

As a simple example consider a function triggering events such as:
300, 301, 304, 299, 2000, 21, 5, we see in foo.c:
% ./foo
Inside foo: x = 300
Inside foo: x = 301
Inside foo: x = 304
Inside foo: x = 299
Inside foo: x = 2000
Inside foo: x = 21
Inside foo: x = 5
% pprof
Reading Profile files in profile.*

NODE 0;CONTEXT 0;THREAD 0:
---------------------------------------------------------------------------------------
%Time    Exclusive    Inclusive       #Call      #Subrs  Inclusive Name
              msec   total msec                          usec/call 
---------------------------------------------------------------------------------------
100.0        0.009        0.145           1           7        145 int main(int, char **) C 
 93.8        0.136        0.136           7           0         19 int foo(int) C 
---------------------------------------------------------------------------------------

USER EVENTS Profile :NODE 0, CONTEXT 0, THREAD 0
---------------------------------------------------------------------------------------
NumSamples   MaxValue   MinValue  MeanValue  Std. Dev.  Event Name
---------------------------------------------------------------------------------------
         1       2000       2000       2000          0  [GROUP=MAX_MARKER] foo counter
         1       2000       2000       2000          0  [GROUP=MAX_MARKER] foo counter : int main(int, char **) C => int foo(int) C 
         2         21          5         13          8  [GROUP=MIN_MARKER] foo counter
         2         21          5         13          8  [GROUP=MIN_MARKER] foo counter : int main(int, char **) C => int foo(int) C 
         7       2000          5      461.4      640.6  foo counter
---------------------------------------------------------------------------------------



Note the new GROUP=MAX or MIN_MARKER annotation. 
