From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5FC4A1F1304; Thu, 5 Feb 2026 21:21:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770326489; cv=none; b=cfVPzL/31IOt91Yd1NPYdiaQjUwWUL+T9UKIT1l1QFYQfx5fDJrtCPfX9mZH0H+1Ia72ygJRsR6O6Q46DMkF+ptWt/cK/jwzs8LgcyasW2fueDyulJs/BlfM3MuCgJtyvDCSlQ6DnjGlwfZ48opzJanUOKsx6yucpP5gXYL0kwM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770326489; c=relaxed/simple; bh=1PNoI7bhktvM3wzSSWLbzCTxNetyB5vQXkVo4AJLmGA=; h=Subject:From:To:Cc:Date:Message-ID:MIME-Version:Content-Type; b=PwR0JBlroDnWzBAeaFGPi1DZLHR3Inkp5lVK5ED0ao40TRXQTkmh7U0C8qTiFsmDCOB6FSpvb8s5zFb3EkmsZyfFZvV8/qVffA9wjRuFBxiMY6G0bpr2+KKbDdpQ2D5C8W2MDwYFrgdVEZHvXl5y/Ge+C2ccvapNpKwPHrhbY7k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XvhXWuSM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XvhXWuSM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B72B7C4CEF7; Thu, 5 Feb 2026 21:21:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770326488; bh=1PNoI7bhktvM3wzSSWLbzCTxNetyB5vQXkVo4AJLmGA=; h=Subject:From:To:Cc:Date:From; b=XvhXWuSM4iLXI/sGecOkj5C2Xcyd4+Bzdk0j9D6SzMSxXC68vesg6XOV2RHJBuGun Ls9wlGOMU01L+ggB/N6NmPQj+WpThfHlYgyrNQSGebMtFBB+cEFrfBZ1zvh6xqOQez O3k/LS2y1A4lv3Ztj1AipNzG2RN+2gXe4e6NfhnVNZtlghE0vIzo55WEzQshOBxG8o UokP/U2MJdu2CQ4ld4tLF3lT/e9P4D4L3Omu9uP4gE3IqcpCud/hUitQgq8LVCEZi9 E9NErAg4bQeVzNmQuEJIUfFuwbtk0tiJg4lQUri6CnvNDKXlXMvmmOjeR4RA0csIc5 8/0TIQD1iKnIQ== Subject: [PATCH net-next v2 0/6] net: sched: refactor qdisc drop reasons into dedicated tracepoint From: Jesper Dangaard Brouer To: netdev@vger.kernel.org, Eric Dumazet , "David S. Miller" , Paolo Abeni , =?utf-8?q?Toke_H=C3=B8iland-J=C3=B8rgensen?= 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 Date: Thu, 05 Feb 2026 22:21:23 +0100 Message-ID: <177032644012.1975497.16411100029657607833.stgit@firesoul> User-Agent: StGit/1.5 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit This series refactors qdisc drop reason handling by introducing a dedicated enum qdisc_drop_reason and trace_qdisc_drop tracepoint, providing qdisc layer drop diagnostics with direct qdisc context visibility. Background: ----------- Identifying which qdisc dropped a packet via skb_drop_reason is difficult. Normally, the kfree_skb tracepoint caller "location" hints at the dropping code, but qdisc drops happen at a central point (__dev_queue_xmit), making this unusable. As a workaround, commits 5765c7f6e317 ("net_sched: sch_fq: add three drop_reason") and a42d71e322a8 ("net_sched: sch_cake: Add drop reasons") encoded qdisc names directly in the drop reason enums. This series provides a cleaner solution by creating a dedicated qdisc tracepoint that naturally includes qdisc context (handle, parent, kind). Solution: --------- Create a new tracepoint trace_qdisc_drop that builds on top of existing trace_qdisc_enqueue infrastructure. It includes qdisc handle, parent, qdisc kind (name), and device information directly. The existing SKB_DROP_REASON_QDISC_DROP is retained for backwards compatibility via kfree_skb_reason(). The qdisc-specific drop reasons (QDISC_DROP_*) provide fine-grained detail via the new tracepoint. The enum uses subsystem encoding (offset by SKB_DROP_REASON_SUBSYS_QDISC) to catch type mismatches for debugging purposes. This implements the alternative approach described in: https://lore.kernel.org/all/6be17a08-f8aa-4f91-9bd0-d9e1f0a92d90@kernel.org/ Changes since RFC v1: --------------------- - Renamed QDISC_DROP_CAKE_FLOOD to QDISC_DROP_FLOOD_PROTECTION (Toke) - Renamed QDISC_DROP_FQ_BAND_LIMIT to QDISC_DROP_BAND_LIMIT - Renamed QDISC_DROP_FQ_HORIZON_LIMIT to QDISC_DROP_HORIZON_LIMIT - Added SKB_DROP_REASON_SUBSYS_QDISC subsystem encoding for enum debugging - Added WARN_ON_ONCE to catch wrong enum type (skb vs qdisc drop reason) - Updated SKB_DROP_REASON_QDISC_DROP doc to reference qdisc:qdisc_drop - Split rename changes into separate patches for clarity Series overview: ---------------- Patch 1: Introduce the qdisc drop reason infrastructure - New enum qdisc_drop_reason with subsystem encoding - New trace_qdisc_drop tracepoint with qdisc context - WARN_ON_ONCE to catch enum type mismatches - Convert FQ, FQ_CoDel, CoDel, SFB, pfifo_fast to use new infrastructure Patch 2: Convert SFQ as example for reviewers - Demonstrates how to convert a flow-based qdisc - Adds QDISC_DROP_MAXFLOWS for flow table exhaustion Patch 3: Fix CAKE to use enum qdisc_drop_reason - Change cobalt_should_drop() return type for type correctness Patch 4: Rename QDISC_DROP_CAKE_FLOOD to QDISC_DROP_FLOOD_PROTECTION - Generic name without embedding qdisc name Patch 5: Rename QDISC_DROP_FQ_* to generic names - QDISC_DROP_FQ_BAND_LIMIT -> QDISC_DROP_BAND_LIMIT - QDISC_DROP_FQ_HORIZON_LIMIT -> QDISC_DROP_HORIZON_LIMIT Patch 6: DualPI2 use qdisc_dequeue_drop() for dequeue drops - Demonstrates dequeue-time drop handling with trace_qdisc_drop --- Jesper Dangaard Brouer (6): net: sched: introduce qdisc-specific drop reason tracing net: sched: sfq: convert to qdisc drop reasons net: sched: sch_cake: use enum qdisc_drop_reason for cobalt_should_drop net: sched: rename QDISC_DROP_CAKE_FLOOD to QDISC_DROP_FLOOD_PROTECTION net: sched: rename QDISC_DROP_FQ_* to generic names net: sched: sch_dualpi2: use qdisc_dequeue_drop() for dequeue drops include/net/dropreason-core.h | 48 ++------------- include/net/dropreason-qdisc.h | 106 +++++++++++++++++++++++++++++++++ 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 | 26 ++++---- net/sched/sch_codel.c | 5 +- net/sched/sch_dualpi2.c | 17 +++--- 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 +- net/sched/sch_sfq.c | 8 +-- 18 files changed, 256 insertions(+), 108 deletions(-) create mode 100644 include/net/dropreason-qdisc.h --