diff options
| -rw-r--r-- | include/uapi/linux/pkt_sched.h | 1 | ||||
| -rw-r--r-- | net/sched/sch_fq_codel.c | 64 |
2 files changed, 46 insertions, 19 deletions
diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h index 1c78c7454c7c..a11afecd4482 100644 --- a/include/uapi/linux/pkt_sched.h +++ b/include/uapi/linux/pkt_sched.h @@ -718,6 +718,7 @@ enum { TCA_FQ_CODEL_FLOWS, TCA_FQ_CODEL_QUANTUM, TCA_FQ_CODEL_CE_THRESHOLD, + TCA_FQ_CODEL_DROP_BATCH_SIZE, __TCA_FQ_CODEL_MAX }; diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c index a5e420b3d4ab..e7b42b0d5145 100644 --- a/net/sched/sch_fq_codel.c +++ b/net/sched/sch_fq_codel.c @@ -59,6 +59,7 @@ struct fq_codel_sched_data { u32 flows_cnt; /* number of flows */ u32 perturbation; /* hash perturbation */ u32 quantum; /* psched_mtu(qdisc_dev(sch)); */ + u32 drop_batch_size; struct codel_params cparams; struct codel_stats cstats; u32 drop_overlimit; @@ -135,17 +136,20 @@ static inline void flow_queue_add(struct fq_codel_flow *flow, skb->next = NULL; } -static unsigned int fq_codel_drop(struct Qdisc *sch) +static unsigned int fq_codel_drop(struct Qdisc *sch, unsigned int max_packets) { struct fq_codel_sched_data *q = qdisc_priv(sch); struct sk_buff *skb; unsigned int maxbacklog = 0, idx = 0, i, len; struct fq_codel_flow *flow; + unsigned int threshold; - /* Queue is full! Find the fat flow and drop packet from it. + /* Queue is full! Find the fat flow and drop packet(s) from it. * This might sound expensive, but with 1024 flows, we scan * 4KB of memory, and we dont need to handle a complex tree * in fast path (packet queue/enqueue) with many cache misses. + * In stress mode, we'll try to drop 64 packets from the flow, + * amortizing this linear lookup to one cache line per drop. */ for (i = 0; i < q->flows_cnt; i++) { if (q->backlogs[i] > maxbacklog) { @@ -153,15 +157,24 @@ static unsigned int fq_codel_drop(struct Qdisc *sch) idx = i; } } + + /* Our goal is to drop half of this fat flow backlog */ + threshold = maxbacklog >> 1; + flow = &q->flows[idx]; - skb = dequeue_head(flow); - len = qdisc_pkt_len(skb); + len = 0; + i = 0; + do { + skb = dequeue_head(flow); + len += qdisc_pkt_len(skb); + kfree_skb(skb); + } while (++i < max_packets && len < threshold); + + flow->dropped += i; q->backlogs[idx] -= len; - sch->q.qlen--; - qdisc_qstats_drop(sch); - qdisc_qstats_backlog_dec(sch, skb); - kfree_skb(skb); - flow->dropped++; + sch->qstats.drops += i; + sch->qstats.backlog -= len; + sch->q.qlen -= i; return idx; } @@ -170,14 +183,14 @@ static unsigned int fq_codel_qdisc_drop(struct Qdisc *sch) unsigned int prev_backlog; prev_backlog = sch->qstats.backlog; - fq_codel_drop(sch); + fq_codel_drop(sch, 1U); return prev_backlog - sch->qstats.backlog; } static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch) { struct fq_codel_sched_data *q = qdisc_priv(sch); - unsigned int idx, prev_backlog; + unsigned int idx, prev_backlog, prev_qlen; struct fq_codel_flow *flow; int uninitialized_var(ret); @@ -206,16 +219,22 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch) return NET_XMIT_SUCCESS; prev_backlog = sch->qstats.backlog; - q->drop_overlimit++; - /* Return Congestion Notification only if we dropped a packet - * from this flow. + prev_qlen = sch->q.qlen; + + /* fq_codel_drop() is quite expensive, as it performs a linear search + * in q->backlogs[] to find a fat flow. + * So instead of dropping a single packet, drop half of its backlog + * with a 64 packets limit to not add a too big cpu spike here. */ - if (fq_codel_drop(sch) == idx) - return NET_XMIT_CN; + ret = fq_codel_drop(sch, q->drop_batch_size); + + q->drop_overlimit += prev_qlen - sch->q.qlen; - /* As we dropped a packet, better let upper stack know this */ - qdisc_tree_reduce_backlog(sch, 1, prev_backlog - sch->qstats.backlog); - return NET_XMIT_SUCCESS; + /* As we dropped packet(s), better let upper stack know this */ + qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen, + prev_backlog - sch->qstats.backlog); + + return ret == idx ? NET_XMIT_CN : NET_XMIT_SUCCESS; } /* This is the specific function called from codel_dequeue() @@ -335,6 +354,7 @@ static const struct nla_policy fq_codel_policy[TCA_FQ_CODEL_MAX + 1] = { [TCA_FQ_CODEL_FLOWS] = { .type = NLA_U32 }, [TCA_FQ_CODEL_QUANTUM] = { .type = NLA_U32 }, [TCA_FQ_CODEL_CE_THRESHOLD] = { .type = NLA_U32 }, + [TCA_FQ_CODEL_DROP_BATCH_SIZE] = { .type = NLA_U32 }, }; static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt) @@ -386,6 +406,9 @@ static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt) if (tb[TCA_FQ_CODEL_QUANTUM]) q->quantum = max(256U, nla_get_u32(tb[TCA_FQ_CODEL_QUANTUM])); + if (tb[TCA_FQ_CODEL_DROP_BATCH_SIZE]) + q->drop_batch_size = min(1U, nla_get_u32(tb[TCA_FQ_CODEL_DROP_BATCH_SIZE])); + while (sch->q.qlen > sch->limit) { struct sk_buff *skb = fq_codel_dequeue(sch); @@ -431,6 +454,7 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt) sch->limit = 10*1024; q->flows_cnt = 1024; + q->drop_batch_size = 64; q->quantum = psched_mtu(qdisc_dev(sch)); q->perturbation = prandom_u32(); INIT_LIST_HEAD(&q->new_flows); @@ -489,6 +513,8 @@ static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb) q->cparams.ecn) || nla_put_u32(skb, TCA_FQ_CODEL_QUANTUM, q->quantum) || + nla_put_u32(skb, TCA_FQ_CODEL_DROP_BATCH_SIZE, + q->drop_batch_size) || nla_put_u32(skb, TCA_FQ_CODEL_FLOWS, q->flows_cnt)) goto nla_put_failure; |