[PATCH 2/2] perf test stat+shadow_stat.sh: Add threshold for rounding errors

[vmolnaro@redhat.com]

From: Veronika Molnarova <vmolnaro@redhat.com>

The test was failing in specific scenarios due to imperfection of FP
arithmetics. The `bc` command wasn't correctly rounding the result
of division causing the failure.

Replace the `bc` with `awk` which should work with more decimal
places and add a threshold to catch any possible rounding errors.
The acceptable rounding error is set to 0.01 when the test
passes with a warning message.
---
 tools/perf/tests/shell/stat+shadow_stat.sh | 30 +++++++++++++++++-----
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/tools/perf/tests/shell/stat+shadow_stat.sh b/tools/perf/tests/shell/stat+shadow_stat.sh
index 0e9cba84e75..73c990fe5ee 100755
--- a/tools/perf/tests/shell/stat+shadow_stat.sh
+++ b/tools/perf/tests/shell/stat+shadow_stat.sh
@@ -4,6 +4,8 @@
 
 set -e
 
+TRESHOLD=0.015
+
 # skip if system-wide mode is forbidden
 perf stat -a true > /dev/null 2>&1 || exit 2
 
@@ -33,10 +35,18 @@ test_global_aggr()
 		fi
 
 		# use printf for rounding and a leading zero
-		res=`printf "%.2f" "$(echo "scale=6; $num / $cyc" | bc -q)"`
+		res=`echo $num $cyc | awk '{printf "%.2f", $1 / $2}'`
 		if [ "$ipc" != "$res" ]; then
-			echo "IPC is different: $res != $ipc  ($num / $cyc)"
-			exit 1
+			# check the difference from the real result for FP imperfections
+			diff=`echo $ipc $res $TRESHOLD | \
+			awk '{x = ($1 - $2) < 0 ? ($2 - $1) : ($1 - $2); print (x > $3)}'`
+
+			if [ $diff -eq 1 ]; then
+				echo "IPC is different: $res != $ipc  ($num / $cyc)"
+				exit 1
+			fi
+
+			echo "Warning: Difference of IPC is under the treshold"
 		fi
 	done
 }
@@ -67,10 +77,18 @@ test_no_aggr()
 		fi
 
 		# use printf for rounding and a leading zero
-		res=`printf "%.2f" "$(echo "scale=6; $num / $cyc" | bc -q)"`
+		res=`echo $num $cyc | awk '{printf "%.2f", $1 / $2}'`
 		if [ "$ipc" != "$res" ]; then
-			echo "IPC is different for $cpu: $res != $ipc  ($num / $cyc)"
-			exit 1
+			# check difference from the real result for FP imperfections
+			diff=`echo $ipc $res $TRESHOLD | \
+			awk '{x = ($1 - $2) < 0 ? ($2 - $1) : ($1 - $2); print (x > $3)}'`
+
+			if [ $diff -eq 1 ]; then
+				echo "IPC is different: $res != $ipc  ($num / $cyc)"
+				exit 1
+			fi
+
+			echo "Warning: Difference of IPC is under the treshold"
 		fi
 	done
 }
-- 
2.41.0