On 7/8/20 9:38 AM, YU, Xiangning wrote:
> Lockless Token Bucket (LTB) is a qdisc implementation that controls the
> use of outbound bandwidth on a shared link. With the help of lockless
> qdisc, and by decoupling rate limiting and bandwidth sharing, LTB is
> designed to scale in the cloud data centers.
> +static int ltb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> + spinlock_t *root_lock, struct sk_buff **to_free)
> +{
> + struct ltb_sched *ltb = qdisc_priv(sch);
> + struct ltb_pcpu_sched *pcpu_q;
> + struct ltb_pcpu_data *pcpu;
> + struct ltb_class *cl;
> + int cpu;
> +
> + pcpu = this_cpu_ptr(ltb->pcpu_data);
> + pcpu_q = qdisc_priv(pcpu->qdisc);
> + cpu = smp_processor_id();
> + ltb_skb_cb(skb)->cpu = cpu;
> +
> + cl = ltb_classify(sch, ltb, skb);
> + if (unlikely(!cl)) {
> + kfree_skb(skb);
> + return NET_XMIT_DROP;
> + }
> +
> + pcpu->active = true;
> + if (unlikely(kfifo_put(&cl->aggr_queues[cpu], skb) == 0)) {
> + kfree_skb(skb);
> + atomic64_inc(&cl->stat_drops);
qdisc drop counter should also be incremented.
> + return NET_XMIT_DROP;
> + }
> +
> + sch->q.qlen = 1;
So, this is touching a shared cache line, why is it needed ? This looks some
hack to me.
> + pcpu_q->qdisc->q.qlen++;
> + tasklet_schedule(&cl->aggr_tasklet);
This is also touching a cache line.
I really have doubts about scheduling a tasklet for every sent packet.
(Particularly if majority of packets should not be rate limited)
