[PATCH net-next 2/4] net_sched: fq_codel: cache skb->truesize into skb->cb

[Eric Dumazet]

Now we defer skb drops, it makes sense to keep a copy
of skb->truesize in struct codel_skb_cb to avoid one
cache line miss per dropped skb in fq_codel_drop(),
to reduce latencies a bit further.

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 include/net/codel_qdisc.h | 1 +
 net/sched/sch_fq_codel.c  | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/net/codel_qdisc.h b/include/net/codel_qdisc.h
index 8144d9cd2908..098630f83a55 100644
--- a/include/net/codel_qdisc.h
+++ b/include/net/codel_qdisc.h
@@ -52,6 +52,7 @@
 /* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
 struct codel_skb_cb {
        codel_time_t enqueue_time;
+       unsigned int mem_usage;
 };
 
 static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index f715195459c9..a5ea0e9b6be4 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -172,7 +172,7 @@ static unsigned int fq_codel_drop(struct Qdisc *sch, 
unsigned int max_packets,
        do {
                skb = dequeue_head(flow);
                len += qdisc_pkt_len(skb);
-               mem += skb->truesize;
+               mem += get_codel_cb(skb)->mem_usage;
                __qdisc_drop(skb, to_free);
        } while (++i < max_packets && len < threshold);
 
@@ -216,7 +216,8 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct 
Qdisc *sch,
                flow->deficit = q->quantum;
                flow->dropped = 0;
        }
-       q->memory_usage += skb->truesize;
+       get_codel_cb(skb)->mem_usage = skb->truesize;
+       q->memory_usage += get_codel_cb(skb)->mem_usage;
        memory_limited = q->memory_usage > q->memory_limit;
        if (++sch->q.qlen <= sch->limit && !memory_limited)
                return NET_XMIT_SUCCESS;
@@ -267,7 +268,7 @@ static struct sk_buff *dequeue_func(struct codel_vars 
*vars, void *ctx)
        if (flow->head) {
                skb = dequeue_head(flow);
                q->backlogs[flow - q->flows] -= qdisc_pkt_len(skb);
-               q->memory_usage -= skb->truesize;
+               q->memory_usage -= get_codel_cb(skb)->mem_usage;
                sch->q.qlen--;
                sch->qstats.backlog -= qdisc_pkt_len(skb);
        }
-- 
2.8.0.rc3.226.g39d4020