From a3d91b2c6f6b8ef88785bf8d2fba74916af6c7c5 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Tue, 7 Feb 2023 15:54:36 +0200 Subject: [PATCH] net/sched: taprio: warn about missing size table Vinicius intended taprio to take the L1 overhead into account when estimating packet transmission time through user input, specifically through the qdisc size table (man tc-stab). Something like this: tc qdisc replace dev $eth root stab overhead 24 taprio \ num_tc 8 \ map 0 1 2 3 4 5 6 7 \ queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \ base-time 0 \ sched-entry S 0x7e 9000000 \ sched-entry S 0x82 1000000 \ max-sdu 0 0 0 0 0 0 0 200 \ flags 0x0 clockid CLOCK_TAI Without the overhead being specified, transmission times will be underestimated and will cause late transmissions. For an offloading driver, it might even cause TX hangs if there is no open gate large enough to send the maximum sized packets for that TC (including L1 overhead). Properly knowing the L1 overhead will ensure that we are able to auto-calculate the queueMaxSDU per traffic class just right, and avoid these hangs due to head-of-line blocking. We can't make the stab mandatory due to existing setups, but we can warn the user that it's important with a warning netlink extack. Link: https://patchwork.kernel.org/project/netdevbpf/patch/20220505160357.298794-1-vladimir.oltean@nxp.com/ Signed-off-by: Vladimir Oltean Reviewed-by: Kurt Kanzenbach Signed-off-by: David S. Miller --- net/sched/sch_taprio.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index e625f8f8704f..7553bc82cf6f 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -1690,6 +1690,7 @@ static int taprio_new_flags(const struct nlattr *attr, u32 old, static int taprio_change(struct Qdisc *sch, struct nlattr *opt, struct netlink_ext_ack *extack) { + struct qdisc_size_table *stab = rtnl_dereference(sch->stab); struct nlattr *tb[TCA_TAPRIO_ATTR_MAX + 1] = { }; struct sched_gate_list *oper, *admin, *new_admin; struct taprio_sched *q = qdisc_priv(sch); @@ -1842,6 +1843,10 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt, new_admin = NULL; err = 0; + if (!stab) + NL_SET_ERR_MSG_MOD(extack, + "Size table not specified, frame length estimations may be inaccurate"); + unlock: spin_unlock_bh(qdisc_lock(sch));