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[93.23.249.26]) by smtp.gmail.com with ESMTPSA id 13sm6953891wmf.23.2019.03.26.08.43.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Mar 2019 08:43:13 -0700 (PDT) Subject: Re: [PATCH bpf-next 0/7] bpf: Propagate cn to TCP To: Alexei Starovoitov Cc: brakmo , netdev , Martin Lau , Alexei Starovoitov , Daniel Borkmann , Kernel Team References: <20190323080542.173569-1-brakmo@fb.com> <704cb63c-13cd-f0ed-d546-18e3596bb63d@gmail.com> <20190323154124.gorqpaqex7ihfs6d@ast-mbp> <0841fe0d-7fcd-bb59-3694-af9969cec5af@gmail.com> <20190324161911.h5eotv2j7f5avcpm@ast-mbp> <5aec97f1-545a-f898-fdd9-c5821d5c6e39@gmail.com> <27e91d11-b454-924d-58ab-a68a0aade906@gmail.com> <20190326042704.7szakyos3ofemowl@ast-mbp> <000fc167-2653-7d3b-80d7-3feba06767cc@gmail.com> <20190326150712.4zi6idzva3ivaupg@ast-mbp> From: Eric Dumazet Message-ID: Date: Tue, 26 Mar 2019 08:43:11 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190326150712.4zi6idzva3ivaupg@ast-mbp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 03/26/2019 08:07 AM, Alexei Starovoitov wrote: > so after 20+ years linux qdisc design is wrong? Yes it is how it is, return values can not be propagated back to the TCP stack in all cases. When a packet is queued to Qdisc 1, there is no way we can return a value that can represent what the packet becomes when dequeued later and queued into Qdisc 2. Also some qdisc take their drop decision later (eg : codel and fq_codel), so ->enqueue() will return a success which might be a lie. > bpf is about choice. We have to give people tools to experiment even > when we philosophically disagree on the design. Maybe, but I feel that for the moment, the choice is only for FB, and rest of the world has to re-invent private ebpf code in order to benefit from all of this. I doubt many TCP users will have the skills/money to benefit from this. Meanwhile, we as a community have to maintain a TCP/IP stack with added hooks and complexity. It seems TCP stack became a playground for experiments.