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Miller" In-Reply-To: <20241210172802.410c76a6@kernel.org> References: <20241209-cake-drop-reason-v1-1-19205f6d1f19@redhat.com> <20241209155157.6a817bc5@kernel.org> <87a5d46i9c.fsf@toke.dk> <20241210172802.410c76a6@kernel.org> X-Clacks-Overhead: GNU Terry Pratchett Date: Wed, 11 Dec 2024 10:55:03 +0100 Message-ID: <87sequ5ytk.fsf@toke.dk> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ldQDAUqkSUxCTtXxnsm2DV36A-NwxFkuRf7r6l1cffE_1733910905 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: Wed, 11 Dec 2024 09:55:10 -0000 Jakub Kicinski writes: > On Tue, 10 Dec 2024 09:42:55 +0100 Toke H=C3=B8iland-J=C3=B8rgensen wrote= : >> > While I initially agreed with making this generic, preserving the qdis= c from >> > where the drop came lets you safely inspect the cb block (timestamp, e= tc), >> > 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. =20 >>=20 >> Yeah, I agree that a generic "dropped by AQM" reason will be too generic >> without knowing which qdisc dropped it. > > Why does type of the qdisc matter if the qdisc was overlimit? Well, I was thinking you'd want to figure out which device it was dropped from, but I guess you have skb->dev for that (and counters). >> 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? > > Can you tell me why I'd need to inspect the skb->cb[] in cake if packet > is overlimit? Actually, none of the fields of the cb are initialized > when the packet is dropped for overlimit, AFAIU. > > If someone is doing serious / advanced debug they mostly care about > access to the qdisc and can trivially check if its ops match the > expected symbol. (Speaking from experience, I've been debugging FQ > packet loss on Nov 23rd.) > > If someone is just doing high level drop attribution having to list all > possible qdiscs under "qdisc discard" is purely pain. > > Can we start with OVERLIMIT and CONGESTION as generic values and we can > specialize if anyone has a clear need? OK, I'll respin and drop CAKE from the names of those two... -Toke