net/sched: taprio: dump class stats for the actual q->qdiscs[]

This makes a difference for the software scheduling mode, where
dev_queue->qdisc_sleeping is the same as the taprio root Qdisc itself,
but when we're talking about what Qdisc and stats get reported for a
traffic class, the root taprio isn't what comes to mind, but q->qdiscs[]
is.

To understand the difference, I've attempted to send 100 packets in
software mode through class 8001:5, and recorded the stats before and
after the change.

Here is before:

$ tc -s class show dev eth0
class taprio 8001:1 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:2 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:3 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:4 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:5 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:6 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:7 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:8 root leaf 8001:
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0

and here is after:

class taprio 8001:1 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:2 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:3 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:4 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:5 root
 Sent 9400 bytes 100 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:6 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:7 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0
class taprio 8001:8 root leaf 800d:
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 window_drops 0

The most glaring (and expected) difference is that before, all class
stats reported the global stats, whereas now, they really report just
the counters for that traffic class.

Finally, Pedro Tammela points out that there is a tc selftest which
checks specifically which handle do the child Qdiscs corresponding to
each class have. That's changing here - taprio no longer reports
tcm->tcm_info as the same handle "1:" as itself (the root Qdisc), but 0
(the handle of the default pfifo child Qdiscs). Since iproute2 does not
print a child Qdisc handle of 0, adjust the test's expected output.

Link: https://lore.kernel.org/netdev/3b83fcf6-a5e8-26fb-8c8a-ec34ec4c3342@mojatatu.com/Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20230807193324.4128292-6-vladimir.oltean@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/sch_taprio.c

@@ -2472,11 +2472,11 @@ static unsigned long taprio_find(struct Qdisc *sch, u32 classid)
 static int taprio_dump_class(struct Qdisc *sch, unsigned long cl,
 			     struct sk_buff *skb, struct tcmsg *tcm)
 {
-	struct netdev_queue *dev_queue = taprio_queue_get(sch, cl);
+	struct Qdisc *child = taprio_leaf(sch, cl);
 
 	tcm->tcm_parent = TC_H_ROOT;
 	tcm->tcm_handle |= TC_H_MIN(cl);
-	tcm->tcm_info = rtnl_dereference(dev_queue->qdisc_sleeping)->handle;
+	tcm->tcm_info = child->handle;
 
 	return 0;
 }
@@ -2486,16 +2486,14 @@ static int taprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
 	__releases(d->lock)
 	__acquires(d->lock)
 {
-	struct netdev_queue *dev_queue = taprio_queue_get(sch, cl);
+	struct Qdisc *child = taprio_leaf(sch, cl);
 	struct tc_taprio_qopt_offload offload = {
 		.cmd = TAPRIO_CMD_QUEUE_STATS,
 		.queue_stats = {
 			.queue = cl - 1,
 		},
 	};
-	struct Qdisc *child;
 
-	child = rtnl_dereference(dev_queue->qdisc_sleeping);
 	if (gnet_stats_copy_basic(d, NULL, &child->bstats, true) < 0 ||
 	    qdisc_qstats_copy(d, child) < 0)
 		return -1;

tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json

@@ -104,7 +104,7 @@
         "cmdUnderTest": "$TC qdisc add dev $ETH root handle 1: taprio num_tc 3 map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 queues 1@0 1@0 1@0 base-time 1000000000 sched-entry S 01 300000 flags 0x1 clockid CLOCK_TAI",
         "expExitCode": "0",
         "verifyCmd": "$TC class show dev $ETH",
-        "matchPattern": "class taprio 1:[0-9]+ root leaf 1:",
+        "matchPattern": "class taprio 1:[0-9]+ root",
         "matchCount": "8",
         "teardown": [
             "echo \"1\" > /sys/bus/netdevsim/del_device"