[Cake] [PATCH net-next] net_sched: sch_cake: Add drop reasons
Dave Taht
dave.taht at gmail.com
Mon Dec 9 18:14:58 EST 2024
On Mon, Dec 9, 2024 at 4:02 AM Toke Høiland-Jørgensen via Cake
<cake at lists.bufferbloat.net> wrote:
>
> Add three qdisc-specific drop reasons for sch_cake:
>
> 1) SKB_DROP_REASON_CAKE_CONGESTED
> Whenever a packet is dropped by the CAKE AQM algorithm because
> congestion is detected.
>
> 2) SKB_DROP_REASON_CAKE_FLOOD
> Whenever a packet is dropped by the flood protection part of the
> CAKE AQM algorithm (BLUE).
>
> 3) SKB_DROP_REASON_CAKE_OVERLIMIT
> Whenever the total queue limit for a CAKE instance is exceeded and a
> packet is dropped to make room.
>
> Also use the existing SKB_DROP_REASON_QUEUE_PURGE in cake_clear_tin().
>
> Reasons show up as:
>
> perf record -a -e skb:kfree_skb sleep 1; perf script
>
> iperf3 665 [005] 848.656964: skb:kfree_skb: skbaddr=0xffff98168a333500 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x10f0 reason: CAKE_OVERLIMIT
> swapper 0 [001] 909.166055: skb:kfree_skb: skbaddr=0xffff98168280cee0 rx_sk=(nil) protocol=34525 location=cake_dequeue+0x5ef reason: CAKE_CONGESTED
>
> Signed-off-by: Toke Høiland-Jørgensen <toke at redhat.com>
Acked-by: Dave Taht <dave.taht at gmail.com>
> ---
> include/net/dropreason-core.h | 18 ++++++++++++++++++
> net/sched/sch_cake.c | 43 +++++++++++++++++++++++--------------------
> 2 files changed, 41 insertions(+), 20 deletions(-)
>
> diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
> index c29282fabae6cdf9dd79f698b92b4b8f57156b1e..a9be76be11ad67d6cc7175f1a643314a7dcdf0b8 100644
> --- a/include/net/dropreason-core.h
> +++ b/include/net/dropreason-core.h
> @@ -61,6 +61,9 @@
> FN(FQ_BAND_LIMIT) \
> FN(FQ_HORIZON_LIMIT) \
> FN(FQ_FLOW_LIMIT) \
> + FN(CAKE_CONGESTED) \
> + FN(CAKE_FLOOD) \
> + FN(CAKE_OVERLIMIT) \
> FN(CPU_BACKLOG) \
> FN(XDP) \
> FN(TC_INGRESS) \
> @@ -329,6 +332,21 @@ enum skb_drop_reason {
> * exceeds its limits.
> */
> SKB_DROP_REASON_FQ_FLOW_LIMIT,
> + /**
> + * @SKB_DROP_REASON_CAKE_CONGESTED: dropped by the CAKE qdisc AQM
> + * algorithm due to congestion.
> + */
> + SKB_DROP_REASON_CAKE_CONGESTED,
> + /**
> + * @SKB_DROP_REASON_CAKE_FLOOD: dropped by the flood protection part of
> + * CAKE qdisc AQM algorithm (BLUE).
> + */
> + SKB_DROP_REASON_CAKE_FLOOD,
> + /**
> + * @SKB_DROP_REASON_CAKE_OVERLIMIT: dropped by CAKE qdisc when a qdisc
> + * instance exceeds its total buffer size limit.
> + */
> + SKB_DROP_REASON_CAKE_OVERLIMIT,
> /**
> * @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
> diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
> index 8d8b2db4653c0c9f271f9c1953e8c61175d8f76b..a57bdc771dd14e81fb0cdf54ca7890ac96f1e311 100644
> --- a/net/sched/sch_cake.c
> +++ b/net/sched/sch_cake.c
> @@ -484,13 +484,14 @@ static bool cobalt_queue_empty(struct cobalt_vars *vars,
> /* Call this with a freshly dequeued packet for possible congestion marking.
> * Returns true as an instruction to drop the packet, false for delivery.
> */
> -static bool cobalt_should_drop(struct cobalt_vars *vars,
> - struct cobalt_params *p,
> - ktime_t now,
> - struct sk_buff *skb,
> - u32 bulk_flows)
> +static enum skb_drop_reason cobalt_should_drop(struct cobalt_vars *vars,
> + struct cobalt_params *p,
> + ktime_t now,
> + struct sk_buff *skb,
> + u32 bulk_flows)
> {
> - bool next_due, over_target, drop = false;
> + enum skb_drop_reason reason = SKB_NOT_DROPPED_YET;
> + bool next_due, over_target;
> ktime_t schedule;
> u64 sojourn;
>
> @@ -533,7 +534,8 @@ static bool cobalt_should_drop(struct cobalt_vars *vars,
>
> if (next_due && vars->dropping) {
> /* Use ECN mark if possible, otherwise drop */
> - drop = !(vars->ecn_marked = INET_ECN_set_ce(skb));
> + if (!(vars->ecn_marked = INET_ECN_set_ce(skb)))
> + reason = SKB_DROP_REASON_CAKE_CONGESTED;
>
> vars->count++;
> if (!vars->count)
> @@ -556,16 +558,17 @@ static bool cobalt_should_drop(struct cobalt_vars *vars,
> }
>
> /* Simple BLUE implementation. Lack of ECN is deliberate. */
> - if (vars->p_drop)
> - drop |= (get_random_u32() < vars->p_drop);
> + if (vars->p_drop && reason == SKB_NOT_DROPPED_YET &&
> + get_random_u32() < vars->p_drop)
> + reason = SKB_DROP_REASON_CAKE_FLOOD;
>
> /* Overload the drop_next field as an activity timeout */
> if (!vars->count)
> vars->drop_next = ktime_add_ns(now, p->interval);
> - else if (ktime_to_ns(schedule) > 0 && !drop)
> + else if (ktime_to_ns(schedule) > 0 && reason == SKB_NOT_DROPPED_YET)
> vars->drop_next = now;
>
> - return drop;
> + return reason;
> }
>
> static bool cake_update_flowkeys(struct flow_keys *keys,
> @@ -1528,12 +1531,11 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
>
> flow->dropped++;
> b->tin_dropped++;
> - sch->qstats.drops++;
>
> if (q->rate_flags & CAKE_FLAG_INGRESS)
> cake_advance_shaper(q, b, skb, now, true);
>
> - __qdisc_drop(skb, to_free);
> + qdisc_drop_reason(skb, sch, to_free, SKB_DROP_REASON_CAKE_OVERLIMIT);
> sch->q.qlen--;
> qdisc_tree_reduce_backlog(sch, 1, len);
>
> @@ -1926,7 +1928,7 @@ static void cake_clear_tin(struct Qdisc *sch, u16 tin)
> q->cur_tin = tin;
> for (q->cur_flow = 0; q->cur_flow < CAKE_QUEUES; q->cur_flow++)
> while (!!(skb = cake_dequeue_one(sch)))
> - kfree_skb(skb);
> + kfree_skb_reason(skb, SKB_DROP_REASON_QUEUE_PURGE);
> }
>
> static struct sk_buff *cake_dequeue(struct Qdisc *sch)
> @@ -1934,6 +1936,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
> struct cake_sched_data *q = qdisc_priv(sch);
> struct cake_tin_data *b = &q->tins[q->cur_tin];
> struct cake_host *srchost, *dsthost;
> + enum skb_drop_reason reason;
> ktime_t now = ktime_get();
> struct cake_flow *flow;
> struct list_head *head;
> @@ -2143,12 +2146,12 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
> goto begin;
> }
>
> + reason = cobalt_should_drop(&flow->cvars, &b->cparams, now, skb,
> + (b->bulk_flow_count *
> + !!(q->rate_flags &
> + CAKE_FLAG_INGRESS)));
> /* Last packet in queue may be marked, shouldn't be dropped */
> - if (!cobalt_should_drop(&flow->cvars, &b->cparams, now, skb,
> - (b->bulk_flow_count *
> - !!(q->rate_flags &
> - CAKE_FLAG_INGRESS))) ||
> - !flow->head)
> + if (reason == SKB_NOT_DROPPED_YET || !flow->head)
> break;
>
> /* drop this packet, get another one */
> @@ -2162,7 +2165,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
> b->tin_dropped++;
> qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
> qdisc_qstats_drop(sch);
> - kfree_skb(skb);
> + kfree_skb_reason(skb, reason);
> if (q->rate_flags & CAKE_FLAG_INGRESS)
> goto retry;
> }
>
> ---
> base-commit: 7ea2745766d776866cfbc981b21ed3cfdf50124e
> change-id: 20241205-cake-drop-reason-b1661e1e7f0a
>
> _______________________________________________
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> Cake at lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cake
--
Dave Täht CSO, LibreQos
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