[PATCH net-next] selftests: net: give up on the cmsg_time accuracy on slow machines

[Jakub Kicinski <kuba@xxxxxxxxxx>]

Commit b9d5f5711dd8 ("selftests: net: increase the delay for relative
cmsg_time.sh test") widened the accepted value range 8x but we still
see flakes (at a rate of around 7%).

Return XFAIL for the most timing sensitive test on slow machines.

Before:

  # ./cmsg_time.sh
    Case UDPv4  - TXTIME rel returned '8074us - 7397us < 4000', expected 'OK'
  FAIL - 1/36 cases failed

After:

  # ./cmsg_time.sh
    Case UDPv4  - TXTIME rel returned '1123us - 941us < 500', expected 'OK' (XFAIL)
    Case UDPv6  - TXTIME rel returned '1227us - 776us < 500', expected 'OK' (XFAIL)
  OK

Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
---
CC: shuah@xxxxxxxxxx
CC: linux-kselftest@xxxxxxxxxxxxxxx
CC: willemdebruijn.kernel@xxxxxxxxx
---
 tools/testing/selftests/net/cmsg_time.sh | 35 +++++++++++++++++-------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/net/cmsg_time.sh b/tools/testing/selftests/net/cmsg_time.sh
index 1d7e756644bc..478af0aefa97 100755
--- a/tools/testing/selftests/net/cmsg_time.sh
+++ b/tools/testing/selftests/net/cmsg_time.sh
@@ -34,13 +34,28 @@ BAD=0
 TOTAL=0
 
 check_result() {
+    local ret=$1
+    local got=$2
+    local exp=$3
+    local case=$4
+    local xfail=$5
+    local xf=
+    local inc=
+
+    if [ "$xfail" == "xfail" ]; then
+	xf="(XFAIL)"
+	inc=0
+    else
+	inc=1
+    fi
+
     ((TOTAL++))
-    if [ $1 -ne 0 ]; then
-	echo "  Case $4 returned $1, expected 0"
-	((BAD++))
+    if [ $ret -ne 0 ]; then
+	echo "  Case $case returned $ret, expected 0 $xf"
+	((BAD+=inc))
     elif [ "$2" != "$3" ]; then
-	echo "  Case $4 returned '$2', expected '$3'"
-	((BAD++))
+	echo "  Case $case returned '$got', expected '$exp' $xf"
+	((BAD+=inc))
     fi
 }
 
@@ -66,14 +81,14 @@ for i in "-4 $TGT4" "-6 $TGT6"; do
 		 awk '/SND/ { if ($3 > 1000) print "OK"; }')
 	check_result $? "$ts" "OK" "$prot - TXTIME abs"
 
-	[ "$KSFT_MACHINE_SLOW" = yes ] && delay=8000 || delay=1000
+	[ "$KSFT_MACHINE_SLOW" = yes ] && xfail=xfail
 
-	ts=$(ip netns exec $NS ./cmsg_sender -p $p $i 1234 -t -d $delay |
+	ts=$(ip netns exec $NS ./cmsg_sender -p $p $i 1234 -t -d 1000 |
 		 awk '/SND/ {snd=$3}
 		      /SCHED/ {sch=$3}
-		      END { if (snd - sch > '$((delay/2))') print "OK";
-			    else print snd, "-", sch, "<", '$((delay/2))'; }')
-	check_result $? "$ts" "OK" "$prot - TXTIME rel"
+		      END { if (snd - sch > 500) print "OK";
+			    else print snd, "-", sch, "<", 500; }')
+	check_result $? "$ts" "OK" "$prot - TXTIME rel" $xfail
     done
 done
 
-- 
2.48.0