Subject: Re: [PATCH v2 net-next] net_sched: sch_fq: add three drop_reason

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 05 Dec 2024 12:57:06 +0100

Eric Dumazet <[email-masked]> writes:

> 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 <[email-masked]>

Nice to see qdisc-specific drop reasons - guess I should look at this
for sch_cake as well!

Reviewed-by: Toke Høiland-Jørgensen <[email-masked]>