selftests/ftrace: Limit length in subsystem-enable tests

While sched* events being traced and sched* events continuously happen,
"[xx] event tracing - enable/disable with subsystem level files" would
not stop as on some slower systems it seems to take forever.
Select the first 100 lines of output would be enough to judge whether
there are more than 3 types of sched events.

Fixes: 815b18e ("ftracetest: Add basic event tracing test cases")
Cc: [email protected]
Signed-off-by: Yuanhe Shu <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Acked-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

Author: Yuanhe Shu

tools/testing/selftests/ftrace/test.d/event/subsystem-enable.tc

@@ -18,7 +18,7 @@ echo 'sched:*' > set_event
 
 yield
 
-count=`cat trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
+count=`head -n 100 trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
 if [ $count -lt 3 ]; then
     fail "at least fork, exec and exit events should be recorded"
 fi
@@ -29,7 +29,7 @@ echo 1 > events/sched/enable
 
 yield
 
-count=`cat trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
+count=`head -n 100 trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
 if [ $count -lt 3 ]; then
     fail "at least fork, exec and exit events should be recorded"
 fi
@@ -40,7 +40,7 @@ echo 0 > events/sched/enable
 
 yield
 
-count=`cat trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
+count=`head -n 100 trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
 if [ $count -ne 0 ]; then
     fail "any of scheduler events should not be recorded"
 fi