[PATCH net-next 2/2] selftests: tc-testing: add DRR deficit refill regression tests

[Victor Nogueira <victor@mojatatu.com>]

Add two DRR cases.

The first asserts the post-dequeue deficit of a class with quantum 256
after one 1514-byte packet is serviced: 256 +
DIV_ROUND_UP(1514 - 256, 256) * 256 - 1514 = 22 bytes, read via
'tc -s class show' while a second packet is still queued behind a
netem-delayed child qdisc.

The second guards the service order of a multi-class round: with two
active quantum-256 classes, the list head holding a 1514-byte packet
and the next class a 514-byte one, the small packet becomes eligible
first and is the one dequeued. A per-class bulk refill that advances
each class to its own eligibility point would dequeue the head class
instead.

The two cases verify differently on purpose: the deficit case reads an
xstats field that tc prints only through its FP format string (it is
not present in JSON output at all), so it must use matchPattern; the
order case asserts the class stats and uses matchJSON for the richer
backlog/qlen coverage.

Both cases use a netem child under DRR, which peeks NULL until its
delay expires, so both emit a rate-limited
"drr_dequeue: qdisc ... is non-work-conserving?" line into dmesg.
That is pre-existing behaviour for any netem-under-classful test
(the infra 1f1f case does the same) and is expected, not a failure.

Both cases assert the loop-equivalence invariant (deficit convergence
and service order) and pass on the unpatched kernel by construction;
they pin it against a future rewrite.

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 .../tc-testing/tc-tests/qdiscs/drr.json       | 82 +++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/drr.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/drr.json
index 2b61d8d79bde..bb0995d8358f 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/drr.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/drr.json
@@ -86,5 +86,87 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY root"
         ]
+    },
+    {
+        "id": "3f3e",
+        "name": "DRR deficit refill converges to the loop-equivalent value",
+        "category": [
+            "qdisc",
+            "drr"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP addr add 10.10.11.10/24 dev $DUMMY",
+            "$TC qdisc add dev $DUMMY root handle 1: drr",
+            "$TC class add dev $DUMMY parent 1: classid 1:1 drr quantum 256",
+            "$TC qdisc add dev $DUMMY parent 1:1 handle 10: netem delay 2s limit 10",
+            "$TC filter add dev $DUMMY parent 1: protocol ip prio 1 u32 match u32 0 0 flowid 1:1",
+            "ping -c 2 -s 1472 -i 1 10.10.11.11 -I $DUMMY -W 0.01 >/dev/null 2>&1 &"
+        ],
+        "cmdUnderTest": "sleep 2.5",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -s class show dev $DUMMY",
+        "matchPattern": "deficit 22b",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY root"
+        ]
+    },
+    {
+        "id": "57a1",
+        "name": "DRR skips only rounds where no class can dequeue (keeps order)",
+        "category": [
+            "qdisc",
+            "drr"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP addr add 10.10.11.10/24 dev $DUMMY",
+            "$TC qdisc add dev $DUMMY root handle 1: drr",
+            "$TC class add dev $DUMMY parent 1: classid 1:1 drr quantum 256",
+            "$TC class add dev $DUMMY parent 1: classid 1:2 drr quantum 256",
+            "$TC qdisc add dev $DUMMY parent 1:1 handle 10: netem delay 2s limit 10",
+            "$TC qdisc add dev $DUMMY parent 1:2 handle 20: netem delay 2s limit 10",
+            "$TC filter add dev $DUMMY parent 1: protocol ip prio 1 u32 match ip dport 1111 0xffff flowid 1:1",
+            "$TC filter add dev $DUMMY parent 1: protocol ip prio 1 u32 match ip dport 2222 0xffff flowid 1:2",
+            "python3 -c \"import socket; a=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); b=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); a.sendto(b'A'*1472,('10.10.11.11',1111)); b.sendto(b'B'*472,('10.10.11.11',2222))\" >/dev/null 2>&1 &",
+            "sleep 1",
+            "python3 -c \"import socket; a=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); b=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); a.sendto(b'A'*1472,('10.10.11.11',1111)); b.sendto(b'B'*472,('10.10.11.11',2222))\" >/dev/null 2>&1 &"
+        ],
+        "cmdUnderTest": "sleep 1.5",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -j -s class show dev $DUMMY",
+        "matchJSON": [
+            {
+                "class": "drr",
+                "handle": "1:1",
+                "root": true,
+                "stats": {
+                    "bytes": 0,
+                    "packets": 0,
+                    "backlog": 3028,
+                    "qlen": 2
+                }
+            },
+            {
+                "class": "drr",
+                "handle": "1:2",
+                "root": true,
+                "stats": {
+                    "bytes": 514,
+                    "packets": 1,
+                    "backlog": 514,
+                    "qlen": 1
+                }
+            }
+        ],
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY root"
+        ]
     }
 ]
-- 
2.43.0