selftests: net: give up on the cmsg_time accuracy on slow machines

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

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250116020105.931338-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/cmsg_time.sh b/tools/testing/selftests/net/cmsg_time.sh
index 1d7e756644bc1ff15af7ad3c0fdd5bac13b00e97..478af0aefa976a5828d30e65a3113ec2a541e0ea 100755 (executable)
--- 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