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Subject[PATCH BUGFIX 3/6] pkt_sched: serve activated aggregates immediately if the scheduler is empty
Date
If no aggregate is in service, then the function qfq_dequeue() does
not dequeue any packet. For this reason, to guarantee QFQ+ to be work
conserving, a just-activated aggregate must be set as in service
immediately if it happens to be the only active aggregate.
This is done by the function qfq_enqueue().

Unfortunately, the function qfq_add_to_agg(), used to add a class to
an aggregate, does not perform this important additional operation.
In particular, if: 1) qfq_add_to_agg() is invoked to complete the move
of a class from a source aggregate, becoming, for this move, inactive,
to a destination aggregate, becoming instead active, and 2) the
destination aggregate becomes the only active aggregate, then this
aggregate is not however set as in service. QFQ+ remains then in a
non-work-conserving state until a new invocation of qfq_enqueue()
recovers the situation.

This fix solves the problem by moving the logic for setting an
aggregate as in service directly into the function qfq_activate_agg().
Hence, from whatever point qfq_activate_aggregate() is invoked, QFQ+
remains work conserving. Since the more-complex logic of this new
version of activate_aggregate() is not necessary, in qfq_dequeue(), to
reschedule an aggregate that finishes its budget, then the aggregate
is now rescheduled by invoking directly the functions needed.

Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Reviewed-by: Fabio Checconi <fchecconi@gmail.com>
---
net/sched/sch_qfq.c | 36 ++++++++++++++++++++++--------------
1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index 4cbbf79..0dbec31 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -1005,6 +1005,12 @@ static inline void charge_actual_service(struct qfq_aggregate *agg)
agg->F = agg->S + (u64)service_received * agg->inv_w;
}

+static inline void qfq_update_agg_ts(struct qfq_sched *q,
+ struct qfq_aggregate *agg,
+ enum update_reason reason);
+
+static void qfq_schedule_agg(struct qfq_sched *q, struct qfq_aggregate *agg);
+
static struct sk_buff *qfq_dequeue(struct Qdisc *sch)
{
struct qfq_sched *q = qdisc_priv(sch);
@@ -1032,7 +1038,7 @@ static struct sk_buff *qfq_dequeue(struct Qdisc *sch)
in_serv_agg->initial_budget = in_serv_agg->budget =
in_serv_agg->budgetmax;

- if (!list_empty(&in_serv_agg->active))
+ if (!list_empty(&in_serv_agg->active)) {
/*
* Still active: reschedule for
* service. Possible optimization: if no other
@@ -1043,8 +1049,9 @@ static struct sk_buff *qfq_dequeue(struct Qdisc *sch)
* handle it, we would need to maintain an
* extra num_active_aggs field.
*/
- qfq_activate_agg(q, in_serv_agg, requeue);
- else if (sch->q.qlen == 0) { /* no aggregate to serve */
+ qfq_update_agg_ts(q, in_serv_agg, requeue);
+ qfq_schedule_agg(q, in_serv_agg);
+ } else if (sch->q.qlen == 0) { /* no aggregate to serve */
q->in_serv_agg = NULL;
return NULL;
}
@@ -1228,17 +1235,11 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
cl->deficit = agg->lmax;
list_add_tail(&cl->alist, &agg->active);

- if (list_first_entry(&agg->active, struct qfq_class, alist) != cl)
- return err; /* aggregate was not empty, nothing else to do */
-
- /* recharge budget */
- agg->initial_budget = agg->budget = agg->budgetmax;
+ if (list_first_entry(&agg->active, struct qfq_class, alist) != cl ||
+ q->in_serv_agg == agg)
+ return err; /* non-empty or in service, nothing else to do */

- qfq_update_agg_ts(q, agg, enqueue);
- if (q->in_serv_agg == NULL)
- q->in_serv_agg = agg;
- else if (agg != q->in_serv_agg)
- qfq_schedule_agg(q, agg);
+ qfq_activate_agg(q, agg, enqueue);

return err;
}
@@ -1295,8 +1296,15 @@ skip_update:
static void qfq_activate_agg(struct qfq_sched *q, struct qfq_aggregate *agg,
enum update_reason reason)
{
+ agg->initial_budget = agg->budget = agg->budgetmax; /* recharge budg. */
+
qfq_update_agg_ts(q, agg, reason);
- qfq_schedule_agg(q, agg);
+ if (q->in_serv_agg == NULL) { /* no aggr. in service or scheduled */
+ q->in_serv_agg = agg; /* start serving this aggregate */
+ /* update V: to be in service, agg must be eligible */
+ q->oldV = q->V = agg->S;
+ } else if (agg != q->in_serv_agg)
+ qfq_schedule_agg(q, agg);
}

static void qfq_slot_remove(struct qfq_sched *q, struct qfq_group *grp,
--
1.7.9.5


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