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Fri, 06 Feb 2026 01:31:31 -0800 (PST) Received: from alrua-x1.borgediget.toke.dk ([45.145.92.2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48320728ac7sm36880205e9.13.2026.02.06.01.31.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Feb 2026 01:31:31 -0800 (PST) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 595AF4FE19A; Fri, 06 Feb 2026 10:31:30 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Jesper Dangaard Brouer , netdev@vger.kernel.org, Eric Dumazet , "David S. Miller" , Paolo Abeni Cc: Jesper Dangaard Brouer , bpf@vger.kernel.org, Jakub Kicinski , horms@kernel.org, jiri@resnulli.us, edumazet@google.com, xiyou.wangcong@gmail.com, jhs@mojatatu.com, atenart@redhat.com, carges@cloudflare.com, kernel-team@cloudflare.com Subject: Re: [PATCH net-next v2 1/6] net: sched: introduce qdisc-specific drop reason tracing In-Reply-To: <177032649028.1975497.12663177216553780756.stgit@firesoul> References: <177032644012.1975497.16411100029657607833.stgit@firesoul> <177032649028.1975497.12663177216553780756.stgit@firesoul> X-Clacks-Overhead: GNU Terry Pratchett Date: Fri, 06 Feb 2026 10:31:30 +0100 Message-ID: <87sebez099.fsf@toke.dk> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Jesper Dangaard Brouer writes: > Create new enum qdisc_drop_reason and trace_qdisc_drop tracepoint > for qdisc layer drop diagnostics with direct qdisc context visibility. > > The new tracepoint includes qdisc handle, parent, kind (name), and > device information. Existing SKB_DROP_REASON_QDISC_DROP is retained > for backwards compatibility via kfree_skb_reason(). > > Convert FQ, FQ_CoDel, CoDel, SFB, and pfifo_fast to use the new > infrastructure. > > Signed-off-by: Jesper Dangaard Brouer > --- > include/net/dropreason-core.h | 42 ++---------------- > include/net/dropreason-qdisc.h | 94 ++++++++++++++++++++++++++++++++++++++++ > include/net/dropreason.h | 6 +++ > include/net/sch_generic.h | 36 ++++++++++----- > include/trace/events/qdisc.h | 51 ++++++++++++++++++++++ > net/core/dev.c | 8 ++- > net/sched/sch_cake.c | 6 +-- > net/sched/sch_codel.c | 5 +- > net/sched/sch_dualpi2.c | 8 +-- > net/sched/sch_fq.c | 7 +-- > net/sched/sch_fq_codel.c | 4 +- > net/sched/sch_fq_pie.c | 4 +- > net/sched/sch_generic.c | 22 +++++++++ > net/sched/sch_gred.c | 4 +- > net/sched/sch_pie.c | 4 +- > net/sched/sch_red.c | 4 +- > net/sched/sch_sfb.c | 4 +- > 17 files changed, 225 insertions(+), 84 deletions(-) > create mode 100644 include/net/dropreason-qdisc.h > > diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h > index a7b7abd66e21..3d8d284e05c8 100644 > --- a/include/net/dropreason-core.h > +++ b/include/net/dropreason-core.h > @@ -68,12 +68,6 @@ > FN(SECURITY_HOOK) \ > FN(QDISC_DROP) \ > FN(QDISC_BURST_DROP) \ > - FN(QDISC_OVERLIMIT) \ > - FN(QDISC_CONGESTED) \ > - FN(CAKE_FLOOD) \ > - FN(FQ_BAND_LIMIT) \ > - FN(FQ_HORIZON_LIMIT) \ > - FN(FQ_FLOW_LIMIT) \ > FN(CPU_BACKLOG) \ > FN(XDP) \ > FN(TC_INGRESS) \ > @@ -371,8 +365,10 @@ enum skb_drop_reason { > /** @SKB_DROP_REASON_SECURITY_HOOK: dropped due to security HOOK */ > SKB_DROP_REASON_SECURITY_HOOK, > /** > - * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc when packet outputting ( > - * failed to enqueue to current qdisc) > + * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc during enqueue or > + * dequeue. More specific drop reasons are available via the > + * qdisc:qdisc_drop tracepoint, which also provides qdisc handle > + * and name for identifying the source. IIUC, this is not needed, see below: [...] > @@ -37,6 +37,24 @@ > const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops; > EXPORT_SYMBOL(default_qdisc_ops); > > +void tcf_kfree_skb_list(struct sk_buff *skb, struct Qdisc *q, > + struct netdev_queue *txq, > + struct net_device *dev) > +{ > + while (unlikely(skb)) { > + struct sk_buff *next = skb->next; > + enum qdisc_drop_reason reason = tcf_get_qdisc_drop_reason(skb); > + > + prefetch(next); > + /* Catch wrong enum: skb_drop_reason vs qdisc_drop_reason */ > + WARN_ON_ONCE(reason && reason < __QDISC_DROP_REASON); > + trace_qdisc_drop(q, txq, dev, skb, reason); > + kfree_skb_reason(skb, SKB_DROP_REASON_QDISC_DROP); AFAIU, the idea here is that you just pass the same 'reason' value to kfree_skb_reason(). Because of the subsys shift and offset, these will all be unique values, so anyone just watching the old tracepoint will get QDISC_DROP_* reasons with no context, and if you want the context you listen to the qdisc_drop tracepoint. -Toke