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net: sched: sfq: convert to qdisc drop reasons

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Convert SFQ to use the new qdisc-specific drop reason infrastructure.

This patch demonstrates how to convert a flow-based qdisc to use the
new enum qdisc_drop_reason. As part of this conversion:

- Add QDISC_DROP_MAXFLOWS for flow table exhaustion
- Rename FQ_FLOW_LIMIT to generic FLOW_LIMIT, now shared by FQ and SFQ
- Use QDISC_DROP_OVERLIMIT for sfq_drop() when overall limit exceeded
- Use QDISC_DROP_FLOW_LIMIT for per-flow depth limit exceeded

The FLOW_LIMIT reason is now a common drop reason for per-flow limits,
applicable to both FQ and SFQ qdiscs.

Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/177211345946.3011628.12770616071857185664.stgit@firesoul
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jesper Dangaard Brouer 2026-02-26 14:44:19 +01:00 committed by Jakub Kicinski
parent ff2998f29f
commit 3e28f8ad47
3 changed files with 19 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
include/net/dropreason-qdisc.h
View File

@ -9,10 +9,11 @@
FN(GENERIC) \
FN(OVERLIMIT) \
FN(CONGESTED) \
FN(MAXFLOWS) \
FN(CAKE_FLOOD) \
FN(FQ_BAND_LIMIT) \
FN(FQ_HORIZON_LIMIT) \
FN(FQ_FLOW_LIMIT) \
FN(FLOW_LIMIT) \
FNe(MAX)
#undef FN
@ -59,6 +60,13 @@ enum qdisc_drop_reason {
* congestion to the sender and prevent bufferbloat.
*/
QDISC_DROP_CONGESTED,
/**
* @QDISC_DROP_MAXFLOWS: packet dropped because the qdisc's flow
* tracking table is full and no free slots are available to allocate
* for a new flow. This indicates flow table exhaustion in flow-based
* qdiscs that maintain per-flow state (e.g., SFQ).
*/
QDISC_DROP_MAXFLOWS,
/**
* @QDISC_DROP_CAKE_FLOOD: CAKE qdisc dropped packet due to flood
* protection mechanism (BLUE algorithm). This indicates potential
@ -77,10 +85,12 @@ enum qdisc_drop_reason {
*/
QDISC_DROP_FQ_HORIZON_LIMIT,
/**
* @QDISC_DROP_FQ_FLOW_LIMIT: FQ dropped packet because an individual
* flow exceeded its per-flow packet limit.
* @QDISC_DROP_FLOW_LIMIT: packet dropped because an individual flow
* exceeded its per-flow packet/depth limit. Used by FQ and SFQ qdiscs
* to enforce per-flow fairness and prevent a single flow from
* monopolizing queue resources.
*/
QDISC_DROP_FQ_FLOW_LIMIT,
QDISC_DROP_FLOW_LIMIT,
/**
* @QDISC_DROP_MAX: the maximum of qdisc drop reasons, which
* shouldn't be used as a real 'reason' - only for tracing code gen

2
net/sched/sch_fq.c
View File

@ -578,7 +578,7 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
if (unlikely(f->qlen >= q->flow_plimit)) {
q->stat_flows_plimit++;
return qdisc_drop_reason(skb, sch, to_free,
QDISC_DROP_FQ_FLOW_LIMIT);
QDISC_DROP_FLOW_LIMIT);
}
if (fq_flow_is_detached(f)) {

8
net/sched/sch_sfq.c
View File

@ -302,7 +302,7 @@ static unsigned int sfq_drop(struct Qdisc *sch, struct sk_buff **to_free)
sfq_dec(q, x);
sch->q.qlen--;
qdisc_qstats_backlog_dec(sch, skb);
qdisc_drop(skb, sch, to_free);
qdisc_drop_reason(skb, sch, to_free, QDISC_DROP_OVERLIMIT);
return len;
}
@ -363,7 +363,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
if (x == SFQ_EMPTY_SLOT) {
x = q->dep[0].next; /* get a free slot */
if (x >= SFQ_MAX_FLOWS)
return qdisc_drop(skb, sch, to_free);
return qdisc_drop_reason(skb, sch, to_free, QDISC_DROP_MAXFLOWS);
q->ht[hash] = x;
slot = &q->slots[x];
slot->hash = hash;
@ -420,14 +420,14 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
if (slot->qlen >= q->maxdepth) {
congestion_drop:
if (!sfq_headdrop(q))
return qdisc_drop(skb, sch, to_free);
return qdisc_drop_reason(skb, sch, to_free, QDISC_DROP_FLOW_LIMIT);
/* We know we have at least one packet in queue */
head = slot_dequeue_head(slot);
delta = qdisc_pkt_len(head) - qdisc_pkt_len(skb);
sch->qstats.backlog -= delta;
slot->backlog -= delta;
qdisc_drop(head, sch, to_free);
qdisc_drop_reason(head, sch, to_free, QDISC_DROP_FLOW_LIMIT);
slot_queue_add(slot, skb);
qdisc_tree_reduce_backlog(sch, 0, delta);