perf test stat+shadow_stat.sh: Add threshold for rounding errors

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.
Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Acked-by: Michael Petlan <mpetlan@redhat.com>
Link: https://lore.kernel.org/r/20230919150419.23193-1-vmolnaro@redhat.comSigned-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/tests/shell/stat+shadow_stat.sh

@@ -4,6 +4,8 @@
 
 set -e
 
+THRESHOLD=0.015
+
 # skip if system-wide mode is forbidden
 perf stat -a true > /dev/null 2>&1 || exit 2
 
@@ -33,11 +35,19 @@ 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
+			# check the difference from the real result for FP imperfections
+			diff=`echo $ipc $res $THRESHOLD | \
+			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 threshold"
+		fi
 	done
 }
 
@@ -67,11 +77,19 @@ 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)"
+			# check difference from the real result for FP imperfections
+			diff=`echo $ipc $res $THRESHOLD | \
+			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 threshold"
+		fi
 	done
 }