netdev - [PATCH net] net: cbs: Fix software cbs to consider packet

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Message-Id: <20200319075659.3126-1-ye.zh-yuan@socionext.com>
Date:   Thu, 19 Mar 2020 16:56:59 +0900
From:   Zh-yuan Ye <ye.zh-yuan@...ionext.com>
To:     netdev@...r.kernel.org
Cc:     okamoto.satoru@...ionext.com, kojima.masahisa@...ionext.com,
        vinicius.gomes@...el.com, Zh-yuan Ye <ye.zh-yuan@...ionext.com>
Subject: [PATCH net] net: cbs: Fix software cbs to consider packet

Currently the software CBS does not consider the packet sending time
when depleting the credits. It caused the throughput to be
Idleslope[kbps] * (Port transmit rate[kbps] / |Sendslope[kbps]|) where
Idleslope * (Port transmit rate / (Idleslope + |Sendslope|)) is expected.
In order to fix the issue above, this patch takes the time when the
packet sending completes into account by moving the anchor time variable
"last" ahead to the send completion time upon transmission and adding
wait when the next dequeue request comes before the send completion time
of the previous packet.

Signed-off-by: Zh-yuan Ye <ye.zh-yuan@...ionext.com>
---
 net/sched/sch_cbs.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_cbs.c b/net/sched/sch_cbs.c
index b2905b03a432..a78b8a750bd9 100644
--- a/net/sched/sch_cbs.c
+++ b/net/sched/sch_cbs.c
@@ -71,6 +71,7 @@ struct cbs_sched_data {
 	int queue;
 	atomic64_t port_rate; /* in bytes/s */
 	s64 last; /* timestamp in ns */
+	s64 send_completed; /* timestamp in ns */
 	s64 credits; /* in bytes */
 	s32 locredit; /* in bytes */
 	s32 hicredit; /* in bytes */
@@ -181,6 +182,10 @@ static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
 	s64 credits;
 	int len;
 
+	if (now < q->send_completed) {
+		qdisc_watchdog_schedule_ns(&q->watchdog, q->send_completed);
+		return NULL;
+	}
 	if (q->credits < 0) {
 		credits = timediff_to_credits(now - q->last, q->idleslope);
 
@@ -192,7 +197,6 @@ static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
 
 			delay = delay_from_credits(q->credits, q->idleslope);
 			qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);
-
 			q->last = now;
 
 			return NULL;
@@ -212,7 +216,9 @@ static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
 	credits += q->credits;
 
 	q->credits = max_t(s64, credits, q->locredit);
-	q->last = now;
+	q->send_completed = now + div64_s64(len * NSEC_PER_SEC,
+					    atomic64_read(&q->port_rate));
+	q->last = q->send_completed;
 
 	return skb;
 }
-- 
2.20.1