[PATCH v2 net 1/7] net/sched: taprio: fix too early schedules switching

Faizal Rahim
2023-11-07T11:22:03Z

In the current taprio code for dynamic schedule change,
admin/oper schedule switching happens immediately when
should_change_schedules() is true. Then the last entry of
the old admin schedule stops being valid anymore from
taprio_dequeue_from_txq’s perspective.

To solve this, we have to delay the switch_schedules() call via
the new cycle_time_correction variable. The variable serves 2
purposes:
1. Upon entering advance_sched(), if the value is set to a
non-initialized value, it indicates that we need to change
schedule.
2. Store the cycle time correction value which will be used for
negative or positive correction.

Fixes: a3d43c0d56f1 ("taprio: Add support adding an admin schedule")
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
---
net/sched/sch_taprio.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 2e1949de4171..dee103647823 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -41,6 +41,7 @@ static struct static_key_false taprio_have_working_mqprio;
#define TXTIME_ASSIST_IS_ENABLED(flags) ((flags) & TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST)
#define FULL_OFFLOAD_IS_ENABLED(flags) ((flags) & TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
#define TAPRIO_FLAGS_INVALID U32_MAX
+#define INIT_CYCLE_TIME_CORRECTION S64_MIN

struct sched_entry {
/* Durations between this GCL entry and the GCL entry where the
@@ -75,6 +76,7 @@ struct sched_gate_list {
ktime_t cycle_end_time;
s64 cycle_time;
s64 cycle_time_extension;
+ s64 cycle_time_correction;
s64 base_time;
};

@@ -940,8 +942,10 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
admin = rcu_dereference_protected(q->admin_sched,
lockdep_is_held(&q->current_entry_lock));

- if (!oper)
+ if (!oper || oper->cycle_time_correction != INIT_CYCLE_TIME_CORRECTION) {
+ oper->cycle_time_correction = INIT_CYCLE_TIME_CORRECTION;
switch_schedules(q, &admin, &oper);
+ }

/* This can happen in two cases: 1. this is the very first run
* of this function (i.e. we weren't running any schedule
@@ -981,7 +985,7 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
* schedule runs.
*/
end_time = sched_base_time(admin);
- switch_schedules(q, &admin, &oper);
+ oper->cycle_time_correction = 0;
}

next->end_time = end_time;
@@ -1174,6 +1178,7 @@ static int parse_taprio_schedule(struct taprio_sched *q, struct nlattr **tb,
}

taprio_calculate_gate_durations(q, new);
+ new->cycle_time_correction = INIT_CYCLE_TIME_CORRECTION;

return 0;
}
--
2.25.1