[PATCH net-next] net_sched: sch_fq: avoid calling ktime_get_ns() if not needed

[PATCH net-next] net_sched: sch_fq: avoid calling ktime_get_ns() if not needed

[Eric Dumazet]

There are two cases were we can avoid calling ktime_get_ns() :

1) Queue is empty.
2) Internal queue is not empty.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/sched/sch_fq.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 1da8864502d448cfa93a9c02da504af61a1093e5..1a662f2bb7bb7bb5507107f61657d44fa28ca991 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -414,16 +414,21 @@ static void fq_check_throttled(struct fq_sched_data *q, u64 now)
 static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 {
 	struct fq_sched_data *q = qdisc_priv(sch);
-	u64 now = ktime_get_ns();
 	struct fq_flow_head *head;
 	struct sk_buff *skb;
 	struct fq_flow *f;
 	unsigned long rate;
 	u32 plen;
+	u64 now;
+
+	if (!sch->q.qlen)
+		return NULL;
 
 	skb = fq_dequeue_head(sch, &q->internal);
 	if (skb)
 		goto out;
+
+	now = ktime_get_ns();
 	fq_check_throttled(q, now);
 begin:
 	head = &q->new_flows;
-- 
2.19.1.1215.g8438c0b245-goog

Re: [PATCH net-next] net_sched: sch_fq: avoid calling ktime_get_ns() if not needed

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Mon, 19 Nov 2018 17:30:19 -0800

> There are two cases were we can avoid calling ktime_get_ns() :
> 
> 1) Queue is empty.
> 2) Internal queue is not empty.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied.

But just to be clear, if the qdisc is empty we do not need to update
flow credits etc.?

Re: [PATCH net-next] net_sched: sch_fq: avoid calling ktime_get_ns() if not needed

[Eric Dumazet]

On Tue, Nov 20, 2018 at 9:58 AM David Miller <davem@davemloft.net> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
> Date: Mon, 19 Nov 2018 17:30:19 -0800
>
> > There are two cases were we can avoid calling ktime_get_ns() :
> >
> > 1) Queue is empty.
> > 2) Internal queue is not empty.
> >
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
>
> Applied.
>
> But just to be clear, if the qdisc is empty we do not need to update
> flow credits etc.?

That is right, nothing needs to be done.