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Miller" , Jakub Kicinski Cc: netdev , Eric Dumazet , Eric Dumazet , Neal Cardwell , Ingemar Johansson S , Tom Henderson , Bob Briscoe Subject: Re: [PATCH net-next 2/2] fq_codel: implement L4S style ce_threshold_ect1 marking In-Reply-To: <20211014175918.60188-3-eric.dumazet@gmail.com> References: <20211014175918.60188-1-eric.dumazet@gmail.com> <20211014175918.60188-3-eric.dumazet@gmail.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 14 Oct 2021 21:54:23 +0200 Message-ID: <87wnmf1ixc.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Eric Dumazet writes: > From: Eric Dumazet > > Add TCA_FQ_CODEL_CE_THRESHOLD_ECT1 boolean option to select Low Latency, > Low Loss, Scalable Throughput (L4S) style marking, along with ce_threshold. > > If enabled, only packets with ECT(1) can be transformed to CE > if their sojourn time is above the ce_threshold. > > Note that this new option does not change rules for codel law. > In particular, if TCA_FQ_CODEL_ECN is left enabled (this is > the default when fq_codel qdisc is created), ECT(0) packets can > still get CE if codel law (as governed by limit/target) decides so. The ability to have certain packets receive a shallow marking threshold and others regular ECN semantics is no doubt useful. However, given that it is by no means certain how the L4S experiment will pan out (and I for one remain sceptical that the real-world benefits will turn out to match the tech demos), I think it's premature to bake the ECT(1) semantics into UAPI. So how about tying this behaviour to a configurable skb->mark instead? That way users can get the shallow marking behaviour for any subset of packets they want, simply by installing a suitable filter on the qdisc... -Toke