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net_sched: sch_fq: add three drop_reason
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Add three new drop_reason, more precise than generic QDISC_DROP:

"tc -s qd" show aggregate counters, it might be more useful
to use drop_reason infrastructure for bug hunting.

1) SKB_DROP_REASON_FQ_BAND_LIMIT
   Whenever a packet is added while its band limit is hit.
   Corresponding value in "tc -s qd" is bandX_drops XXXX

2) SKB_DROP_REASON_FQ_HORIZON_LIMIT
   Whenever a packet has a timestamp too far in the future.
   Corresponding value in "tc -s qd" is horizon_drops XXXX

3) SKB_DROP_REASON_FQ_FLOW_LIMIT
   Whenever a flow has reached its limit.
   Corresponding value in "tc -s qd" is flows_plimit XXXX

Tested:
tc qd replace dev eth1 root fq flow_limit 10 limit 100000
perf record -a -e skb:kfree_skb sleep 1; perf script

      udp_stream   12329 [004]   216.929492: skb:kfree_skb: skbaddr=0xffff888eabe17e00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT
      udp_stream   12385 [006]   216.929593: skb:kfree_skb: skbaddr=0xffff888ef8827f00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT
      udp_stream   12389 [005]   216.929871: skb:kfree_skb: skbaddr=0xffff888ecb9ba500 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT
      udp_stream   12316 [009]   216.930398: skb:kfree_skb: skbaddr=0xffff888eca286b00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT
      udp_stream   12400 [008]   216.930490: skb:kfree_skb: skbaddr=0xffff888eabf93d00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT

tc qd replace dev eth1 root fq flow_limit 100 limit 10000
perf record -a -e skb:kfree_skb sleep 1; perf script

      udp_stream   18074 [001]  1058.318040: skb:kfree_skb: skbaddr=0xffffa23c881fc000 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT
      udp_stream   18126 [005]  1058.320651: skb:kfree_skb: skbaddr=0xffffa23c6aad4000 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT
      udp_stream   18118 [006]  1058.321065: skb:kfree_skb: skbaddr=0xffffa23df0d48a00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT
      udp_stream   18074 [001]  1058.321126: skb:kfree_skb: skbaddr=0xffffa23c881ffa00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT
      udp_stream   15815 [003]  1058.321224: skb:kfree_skb: skbaddr=0xffffa23c9835db00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT

tc -s -d qd sh dev eth1
qdisc fq 8023: root refcnt 257 limit 10000p flow_limit 100p buckets 1024 orphan_mask 1023
 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 weights 589824 196608 65536 quantum 18Kb
 initial_quantum 92120b low_rate_threshold 550Kbit refill_delay 40ms
 timer_slack 10us horizon 10s horizon_drop
 Sent 492439603330 bytes 336953991 pkt (dropped 61724094, overlimits 0 requeues 4463)
 backlog 14611228b 9995p requeues 4463
  flows 2965 (inactive 1151 throttled 0) band0_pkts 0 band1_pkts 9993 band2_pkts 0
  gc 6347 highprio 0 fastpath 30 throttled 5 latency 2.32us flows_plimit 7403693
 band1_drops 54320401

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20241204171950.89829-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Eric Dumazet authored and kuba-moo committed Dec 6, 2024
1 parent f930594 commit 5765c7f
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Showing 3 changed files with 36 additions and 4 deletions.
18 changes: 18 additions & 0 deletions include/net/dropreason-core.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,9 @@
FN(TC_EGRESS) \
FN(SECURITY_HOOK) \
FN(QDISC_DROP) \
FN(FQ_BAND_LIMIT) \
FN(FQ_HORIZON_LIMIT) \
FN(FQ_FLOW_LIMIT) \
FN(CPU_BACKLOG) \
FN(XDP) \
FN(TC_INGRESS) \
Expand Down Expand Up @@ -311,6 +314,21 @@ enum skb_drop_reason {
* failed to enqueue to current qdisc)
*/
SKB_DROP_REASON_QDISC_DROP,
/**
* @SKB_DROP_REASON_FQ_BAND_LIMIT: dropped by fq qdisc when per band
* limit is reached.
*/
SKB_DROP_REASON_FQ_BAND_LIMIT,
/**
* @SKB_DROP_REASON_FQ_HORIZON_LIMIT: dropped by fq qdisc when packet
* timestamp is too far in the future.
*/
SKB_DROP_REASON_FQ_HORIZON_LIMIT,
/**
* @SKB_DROP_REASON_FQ_FLOW_LIMIT: dropped by fq qdisc when a flow
* exceeds its limits.
*/
SKB_DROP_REASON_FQ_FLOW_LIMIT,
/**
* @SKB_DROP_REASON_CPU_BACKLOG: failed to enqueue the skb to the per CPU
* backlog queue. This can be caused by backlog queue full (see
Expand Down
8 changes: 8 additions & 0 deletions include/net/sch_generic.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1245,6 +1245,14 @@ static inline int qdisc_drop(struct sk_buff *skb, struct Qdisc *sch,
return NET_XMIT_DROP;
}

static inline int qdisc_drop_reason(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free,
enum skb_drop_reason reason)
{
tcf_set_drop_reason(skb, reason);
return qdisc_drop(skb, sch, to_free);
}

static inline int qdisc_drop_all(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
Expand Down
14 changes: 10 additions & 4 deletions net/sched/sch_fq.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -537,6 +537,8 @@ static bool fq_packet_beyond_horizon(const struct sk_buff *skb,
return unlikely((s64)skb->tstamp > (s64)(now + q->horizon));
}

#define FQDR(reason) SKB_DROP_REASON_FQ_##reason

static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
Expand All @@ -548,7 +550,8 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
band = fq_prio2band(q->prio2band, skb->priority & TC_PRIO_MAX);
if (unlikely(q->band_pkt_count[band] >= sch->limit)) {
q->stat_band_drops[band]++;
return qdisc_drop(skb, sch, to_free);
return qdisc_drop_reason(skb, sch, to_free,
FQDR(BAND_LIMIT));
}

now = ktime_get_ns();
Expand All @@ -558,8 +561,9 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
/* Check if packet timestamp is too far in the future. */
if (fq_packet_beyond_horizon(skb, q, now)) {
if (q->horizon_drop) {
q->stat_horizon_drops++;
return qdisc_drop(skb, sch, to_free);
q->stat_horizon_drops++;
return qdisc_drop_reason(skb, sch, to_free,
FQDR(HORIZON_LIMIT));
}
q->stat_horizon_caps++;
skb->tstamp = now + q->horizon;
Expand All @@ -572,7 +576,8 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
if (f != &q->internal) {
if (unlikely(f->qlen >= q->flow_plimit)) {
q->stat_flows_plimit++;
return qdisc_drop(skb, sch, to_free);
return qdisc_drop_reason(skb, sch, to_free,
FQDR(FLOW_LIMIT));
}

if (fq_flow_is_detached(f)) {
Expand All @@ -597,6 +602,7 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,

return NET_XMIT_SUCCESS;
}
#undef FQDR

static void fq_check_throttled(struct fq_sched_data *q, u64 now)
{
Expand Down

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