[RFC net-next v1 4/6] taprio: Add support for cycle-time-extension

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

IEEE 802.1Q-2018 defines the concept of a cycle-time-extension, so the
last entry of a schedule before the start of a new schedule can be
extended, so "too-short" entries can be avoided.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
---
 include/uapi/linux/pkt_sched.h |  1 +
 net/sched/sch_taprio.c         | 35 ++++++++++++++++++++++++++++------
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 7a32276838e1..8b2f993cbb77 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -1168,6 +1168,7 @@ enum {
 	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_SCHED_CYCLE_TIME_EXTENSION, /* s64 */
 	__TCA_TAPRIO_ATTR_MAX,
 };
 
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 70bba9782449..3807aacde26b 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -44,6 +44,7 @@ struct sched_gate_list {
 	size_t num_entries;
 	ktime_t cycle_close_time;
 	s64 cycle_time;
+	s64 cycle_time_extension;
 	s64 base_time;
 };
 
@@ -265,7 +266,7 @@ static bool should_change_schedules(const struct sched_gate_list *admin,
 				    const struct sched_gate_list *oper,
 				    ktime_t close_time)
 {
-	ktime_t next_base_time;
+	ktime_t next_base_time, extension_time;
 
 	if (!admin)
 		return false;
@@ -278,6 +279,20 @@ static bool should_change_schedules(const struct sched_gate_list *admin,
 	if (ktime_compare(next_base_time, close_time) <= 0)
 		return true;
 
+	/* This is the cycle_time_extension case, if the close_time
+	 * plus the amount that can be extended would fall after the
+	 * next schedule base_time, we can extend the current schedule
+	 * for that amount.
+	 */
+	extension_time = ktime_add_ns(close_time, oper->cycle_time_extension);
+
+	/* FIXME: the IEEE 802.1Q-2018 Specification isn't clear about
+	 * how precisely the extension should be made. So after
+	 * conformance testing, this logic may change.
+	 */
+	if (ktime_compare(next_base_time, extension_time) <= 0)
+		return true;
+
 	return false;
 }
 
@@ -366,11 +381,12 @@ static const struct nla_policy taprio_policy[TCA_TAPRIO_ATTR_MAX + 1] = {
 	[TCA_TAPRIO_ATTR_PRIOMAP]	       = {
 		.len = sizeof(struct tc_mqprio_qopt)
 	},
-	[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST]     = { .type = NLA_NESTED },
-	[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 },
+	[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST]           = { .type = NLA_NESTED },
+	[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 },
+	[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION] = { .type = NLA_S64 },
 };
 
 static int fill_sched_entry(struct nlattr **tb, struct sched_entry *entry,
@@ -472,6 +488,9 @@ 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_EXTENSION])
+		new->cycle_time_extension = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION]);
+
 	if (tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME])
 		new->cycle_time = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]);
 
@@ -948,6 +967,10 @@ static int dump_schedule(struct sk_buff *msg,
 			root->cycle_time, TCA_TAPRIO_PAD))
 		return -1;
 
+	if (nla_put_s64(msg, TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION,
+			root->cycle_time_extension, 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