+++ /dev/null
-From: Eric Dumazet <edumazet@google.com>
-Date: Sun, 1 May 2016 16:47:26 -0700
-Subject: [PATCH] fq_codel: add batch ability to fq_codel_drop()
-
-In presence of inelastic flows and stress, we can call
-fq_codel_drop() for every packet entering fq_codel qdisc.
-
-fq_codel_drop() is quite expensive, as it does a linear scan
-of 4 KB of memory to find a fat flow.
-Once found, it drops the oldest packet of this flow.
-
-Instead of dropping a single packet, try to drop 50% of the backlog
-of this fat flow, with a configurable limit of 64 packets per round.
-
-TCA_FQ_CODEL_DROP_BATCH_SIZE is the new attribute to make this
-limit configurable.
-
-With this strategy the 4 KB search is amortized to a single cache line
-per drop [1], so fq_codel_drop() no longer appears at the top of kernel
-profile in presence of few inelastic flows.
-
-[1] Assuming a 64byte cache line, and 1024 buckets
-
-Signed-off-by: Eric Dumazet <edumazet@google.com>
-Reported-by: Dave Taht <dave.taht@gmail.com>
-Cc: Jonathan Morton <chromatix99@gmail.com>
-Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
-Acked-by: Dave Taht
-Signed-off-by: David S. Miller <davem@davemloft.net>
----
-
---- a/include/uapi/linux/pkt_sched.h
-+++ b/include/uapi/linux/pkt_sched.h
-@@ -711,6 +711,7 @@ enum {
- TCA_FQ_CODEL_FLOWS,
- TCA_FQ_CODEL_QUANTUM,
- TCA_FQ_CODEL_CE_THRESHOLD,
-+ TCA_FQ_CODEL_DROP_BATCH_SIZE,
- __TCA_FQ_CODEL_MAX
- };
-
---- a/net/sched/sch_fq_codel.c
-+++ b/net/sched/sch_fq_codel.c
-@@ -57,6 +57,7 @@ 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;
-@@ -133,17 +134,20 @@ static inline void flow_queue_add(struct
- 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) {
-@@ -151,15 +155,24 @@ static unsigned int fq_codel_drop(struct
- 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;
- }
-
-@@ -168,14 +181,14 @@ static unsigned int fq_codel_qdisc_drop(
- 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);
-
-@@ -204,16 +217,22 @@ static int fq_codel_enqueue(struct sk_bu
- 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()
-@@ -323,6 +342,7 @@ static const struct nla_policy fq_codel_
- [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)
-@@ -374,6 +394,9 @@ static int fq_codel_change(struct Qdisc
- 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);
-
-@@ -419,6 +442,7 @@ static int fq_codel_init(struct Qdisc *s
-
- 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);
-@@ -476,6 +500,8 @@ static int fq_codel_dump(struct Qdisc *s
- 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;
projects / openwrt / openwrt.git / blobdiff