[RFC net-next v1 3/6] taprio: Add support for setting the cycle-time manually

[Vinicius Costa Gomes <vinicius.gomes@intel.com>]

IEEE 802.1Q-2018 defines that a the cycle-time of a schedule may be
overridden, so the schedule is truncated to a determined "width".

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
---
 include/uapi/linux/pkt_sched.h |  1 +
 net/sched/sch_taprio.c         | 56 ++++++++++++++++++++++++++++------
 2 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index d59770d0eb84..7a32276838e1 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -1167,6 +1167,7 @@ enum {
 	TCA_TAPRIO_ATTR_SCHED_CLOCKID, /* s32 */
 	TCA_TAPRIO_PAD,
 	TCA_TAPRIO_ATTR_ADMIN_SCHED, /* The admin sched, only used in dump */
+	TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME, /* s64 */
 	__TCA_TAPRIO_ATTR_MAX,
 };
 
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index af12353232a5..70bba9782449 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -42,6 +42,8 @@ struct sched_gate_list {
 	struct rcu_head rcu;
 	struct list_head entries;
 	size_t num_entries;
+	ktime_t cycle_close_time;
+	s64 cycle_time;
 	s64 base_time;
 };
 
@@ -250,7 +252,13 @@ static bool should_restart_cycle(const struct sched_gate_list *oper,
 {
 	WARN_ON(!entry);
 
-	return list_is_last(&entry->list, &oper->entries);
+	if (list_is_last(&entry->list, &oper->entries))
+		return true;
+
+	if (ktime_compare(entry->close_time, oper->cycle_close_time) == 0)
+		return true;
+
+	return false;
 }
 
 static bool should_change_schedules(const struct sched_gate_list *admin,
@@ -306,13 +314,17 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 		goto first_run;
 	}
 
-	if (should_restart_cycle(oper, entry))
+	if (should_restart_cycle(oper, entry)) {
 		next = list_first_entry(&oper->entries, struct sched_entry,
 					list);
-	else
+		oper->cycle_close_time = ktime_add_ns(oper->cycle_close_time,
+						      oper->cycle_time);
+	} else {
 		next = list_next_entry(entry, list);
+	}
 
 	close_time = ktime_add_ns(entry->close_time, next->interval);
+	close_time = min_t(ktime_t, close_time, oper->cycle_close_time);
 
 	if (should_change_schedules(admin, oper, close_time)) {
 		/* Set things so the next time this runs, the new
@@ -358,6 +370,7 @@ static const struct nla_policy taprio_policy[TCA_TAPRIO_ATTR_MAX + 1] = {
 	[TCA_TAPRIO_ATTR_SCHED_BASE_TIME]      = { .type = NLA_S64 },
 	[TCA_TAPRIO_ATTR_SCHED_SINGLE_ENTRY]   = { .type = NLA_NESTED },
 	[TCA_TAPRIO_ATTR_SCHED_CLOCKID]        = { .type = NLA_S32 },
+	[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]     = { .type = NLA_S64 },
 };
 
 static int fill_sched_entry(struct nlattr **tb, struct sched_entry *entry,
@@ -459,6 +472,9 @@ static int parse_taprio_schedule(struct nlattr **tb,
 	if (tb[TCA_TAPRIO_ATTR_SCHED_BASE_TIME])
 		new->base_time = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_BASE_TIME]);
 
+	if (tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME])
+		new->cycle_time = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]);
+
 	if (tb[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST])
 		err = parse_sched_list(
 			tb[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST], new, extack);
@@ -530,22 +546,32 @@ static int taprio_parse_mqprio_opt(struct net_device *dev,
 	return 0;
 }
 
+static ktime_t get_cycle_time(struct sched_gate_list *sched)
+{
+	struct sched_entry *entry;
+	ktime_t cycle = 0;
+
+	if (sched->cycle_time != 0)
+		return sched->cycle_time;
+
+	list_for_each_entry(entry, &sched->entries, list)
+		cycle = ktime_add_ns(cycle, entry->interval);
+
+	sched->cycle_time = cycle;
+
+	return cycle;
+}
+
 static ktime_t taprio_get_start_time(struct Qdisc *sch,
 				     struct sched_gate_list *sched)
 {
 	struct taprio_sched *q = qdisc_priv(sch);
-	struct sched_entry *entry;
 	ktime_t now, base, cycle;
 	s64 n;
 
 	base = ns_to_ktime(sched->base_time);
-	cycle = 0;
-
-	/* Calculate the cycle_time, by summing all the intervals.
-	 */
-	list_for_each_entry(entry, &sched->entries, list)
-		cycle = ktime_add_ns(cycle, entry->interval);
 
+	cycle = get_cycle_time(sched);
 	if (!cycle)
 		return base;
 
@@ -566,10 +592,16 @@ static void setup_first_close_time(struct taprio_sched *q,
 				   struct sched_gate_list *sched, ktime_t base)
 {
 	struct sched_entry *first;
+	ktime_t cycle;
 
 	first = list_first_entry(&sched->entries,
 				 struct sched_entry, list);
 
+	cycle = get_cycle_time(sched);
+
+	/* FIXME: find a better place to do this */
+	sched->cycle_close_time = ktime_add_ns(base, cycle);
+
 	first->close_time = ktime_add_ns(base, first->interval);
 	atomic_set(&first->budget,
 		   (first->interval * 1000) / q->picos_per_byte);
@@ -912,6 +944,10 @@ static int dump_schedule(struct sk_buff *msg,
 			root->base_time, TCA_TAPRIO_PAD))
 		return -1;
 
+	if (nla_put_s64(msg, TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME,
+			root->cycle_time, TCA_TAPRIO_PAD))
+		return -1;
+
 	entry_list = nla_nest_start(msg, TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST);
 	if (!entry_list)
 		goto error_nest;
-- 
2.21.0