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[188.67.132.152]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-300431a561csm9788831fa.116.2024.12.10.01.10.58 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 10 Dec 2024 01:10:59 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) From: Jonathan Morton In-Reply-To: <87a5d46i9c.fsf@toke.dk> Date: Tue, 10 Dec 2024 11:10:57 +0200 Cc: Dave Taht , Jakub Kicinski , Jiri Pirko , netdev@vger.kernel.org, Jamal Hadi Salim , cake@lists.bufferbloat.net, Eric Dumazet , Simon Horman , Cong Wang , Paolo Abeni , "David S. Miller" Content-Transfer-Encoding: quoted-printable Message-Id: References: <20241209-cake-drop-reason-v1-1-19205f6d1f19@redhat.com> <20241209155157.6a817bc5@kernel.org> <87a5d46i9c.fsf@toke.dk> To: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= X-Mailer: Apple Mail (2.3654.100.0.2.22) Subject: Re: [Cake] [PATCH net-next] net_sched: sch_cake: Add drop reasons X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 10 Dec 2024 09:11:02 -0000 > On 10 Dec, 2024, at 10:42 am, Toke H=C3=B8iland-J=C3=B8rgensen via = Cake wrote: >=20 >>> On Mon, 09 Dec 2024 13:02:18 +0100 Toke H=C3=B8iland-J=C3=B8rgensen = wrote: >>>> Add three qdisc-specific drop reasons for sch_cake: >>>>=20 >>>> 1) SKB_DROP_REASON_CAKE_CONGESTED >>>> Whenever a packet is dropped by the CAKE AQM algorithm because >>>> congestion is detected. >>>>=20 >>>> 2) SKB_DROP_REASON_CAKE_FLOOD >>>> Whenever a packet is dropped by the flood protection part of the >>>> CAKE AQM algorithm (BLUE). >>>>=20 >>>> 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. >>>=20 >>> Eric's patch was adding fairly FQ-specific reasons, other than flood >>> this seems like generic AQM stuff, no? =46rom a very quick look the >>> congestion looks like fairly standard AQM, overlimit is also typical >>> for qdics? >>=20 >> While I initially agreed with making this generic, preserving the = qdisc from >> where the drop came lets you safely inspect the cb block (timestamp, = etc), >> format of which varies by qdisc. You also get insight as to which >> qdisc was dropping. >>=20 >> Downside is we'll end up with SKB_DROP_REASON_XXX_OVERLIMIT for >> each of the qdiscs. Etc. >=20 > Yeah, I agree that a generic "dropped by AQM" reason will be too = generic > without knowing which qdisc dropped it. I guess any calls directly to > kfree_skb_reason() from the qdisc will provide the calling function, = but > for qdisc_drop_reason() the drop will be deferred to = __dev_queue_xmit(), > so no way of knowing where the drop came from, AFAICT? Would it make sense to be able to extract a "generic" code by applying a = bitmask? Leave code space for "qdisc specific" reasons within that = mask. Then people who don't care about qdisc internals can still = reliably interpret the codes, even for future qdiscs. - Jonathan Morton=