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Miller" In-Reply-To: References: <20241209-cake-drop-reason-v1-1-19205f6d1f19@redhat.com> <20241209155157.6a817bc5@kernel.org> X-Clacks-Overhead: GNU Terry Pratchett Date: Tue, 10 Dec 2024 09:42:55 +0100 Message-ID: <87a5d46i9c.fsf@toke.dk> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: y4dDnsaj6IpOp4NrSAo5ajZZScBiIJw44JOI3oezdno_1733820178 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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 08:43:00 -0000 Dave Taht writes: > On Mon, Dec 9, 2024 at 3:52=E2=80=AFPM Jakub Kicinski via Cake > wrote: >> >> On Mon, 09 Dec 2024 13:02:18 +0100 Toke H=C3=B8iland-J=C3=B8rgensen wrot= e: >> > 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. >> >> Eric's patch was adding fairly FQ-specific reasons, other than flood >> this seems like generic AQM stuff, no? From a very quick look the >> congestion looks like fairly standard AQM, overlimit is also typical >> for qdics? > > While I initially agreed with making this generic, preserving the qdisc f= rom > 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. > > Downside is we'll end up with SKB_DROP_REASON_XXX_OVERLIMIT for > each of the qdiscs. Etc. 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? -Toke