From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A8E314B960; Wed, 24 Jul 2024 08:16:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721808961; cv=none; b=VWi608EtyJwf0gWNq/8S+L4vV0mxWQjm3KiBtrWO7EwPJSuZOg7dcHQ44Vf4wIdznpWC6FE1m/PzssE/nzbVeHRuBSnOIneQJUHNZWsIU1CBuv8oUqo8SFnuhCxrL0R2xkv49Y2ggVIfH8QbYpedNY1CmavLW5ym4XlKrmjcj94= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721808961; c=relaxed/simple; bh=/mIEHHXkDVq16jXgWsjxyuQ8xG0Avx6YZlNQpXLG+5g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pghAoT1avrZIueycTkZZk7gE/BPXI3KCWLkHq/ILNnvOmZd6E9RWwlUrRcX52ldZWST9gxMMT5onhGh//0Y9hsIC+K1mWyGmahTtbgQtjKsd6pyA4kwz9KBc3tnmX8Jda59oN4SiX2nCDzR7CjjH6BwyFUx1MUx6uyQsr61alYU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BpoyGaeM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BpoyGaeM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F2C1C4AF0B; Wed, 24 Jul 2024 08:15:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721808960; bh=/mIEHHXkDVq16jXgWsjxyuQ8xG0Avx6YZlNQpXLG+5g=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=BpoyGaeMppx7PiTxCI3JUwEm/ucho4ymnpXiklBDXAWWhJ9G05hdRWyZI5qxuiF2M t03P1NxauOLqJkHCMZ+hJzsVN5xKomlDgmJnW4PVVtyUDw1j15ShQ/a0xRq4c01iKt 3VainrhzQvpvVIbEG//NvepFaoma4pf7dogfYHd8InGVnEb0JE5XOqcqq8D9eWihVK k4X78GBh7Y6Mp7B41NMwaFDbAW5dQ49q5ABpC6fK9yBH8QOFse5tfaEaRybB24g/mk K/DvPpTxcsGDFcr+ORI2JG1yuupdJWfpj7V9X9oyFwSxHQ2jTBPPUoKfQMGOwl3k37 oEsdxsNDSkYaQ== Message-ID: <7c992504-51ad-4104-a039-382fe69ff1c8@kernel.org> Date: Wed, 24 Jul 2024 10:15:53 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH net v2 1/2] tcp: process the 3rd ACK with sk_socket for TFO/MPTCP Content-Language: en-GB To: Neal Cardwell Cc: Eric Dumazet , "David S. Miller" , David Ahern , Jakub Kicinski , Paolo Abeni , Kuniyuki Iwashima , netdev@vger.kernel.org, mptcp@lists.linux.dev, linux-kernel@vger.kernel.org References: <20240718-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v2-0-d653f85639f6@kernel.org> <20240718-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v2-1-d653f85639f6@kernel.org> <2583642a-cc5f-4765-856d-4340adcecf33@kernel.org> <4558399b-002b-40ff-8d9b-ac7bf13b3d2e@kernel.org> <9c0b40e5-2137-423f-85c3-385408ea861e@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; keydata= xsFNBFXj+ekBEADxVr99p2guPcqHFeI/JcFxls6KibzyZD5TQTyfuYlzEp7C7A9swoK5iCvf YBNdx5Xl74NLSgx6y/1NiMQGuKeu+2BmtnkiGxBNanfXcnl4L4Lzz+iXBvvbtCbynnnqDDqU c7SPFMpMesgpcu1xFt0F6bcxE+0ojRtSCZ5HDElKlHJNYtD1uwY4UYVGWUGCF/+cY1YLmtfb WdNb/SFo+Mp0HItfBC12qtDIXYvbfNUGVnA5jXeWMEyYhSNktLnpDL2gBUCsdbkov5VjiOX7 CRTkX0UgNWRjyFZwThaZADEvAOo12M5uSBk7h07yJ97gqvBtcx45IsJwfUJE4hy8qZqsA62A nTRflBvp647IXAiCcwWsEgE5AXKwA3aL6dcpVR17JXJ6nwHHnslVi8WesiqzUI9sbO/hXeXw TDSB+YhErbNOxvHqCzZEnGAAFf6ges26fRVyuU119AzO40sjdLV0l6LE7GshddyazWZf0iac nEhX9NKxGnuhMu5SXmo2poIQttJuYAvTVUNwQVEx/0yY5xmiuyqvXa+XT7NKJkOZSiAPlNt6 VffjgOP62S7M9wDShUghN3F7CPOrrRsOHWO/l6I/qJdUMW+MHSFYPfYiFXoLUZyPvNVCYSgs 3oQaFhHapq1f345XBtfG3fOYp1K2wTXd4ThFraTLl8PHxCn4ywARAQABzSRNYXR0aGlldSBC YWVydHMgPG1hdHR0YmVAa2VybmVsLm9yZz7CwZEEEwEIADsCGwMFCwkIBwIGFQoJCAsCBBYC AwECHgECF4AWIQToy4X3aHcFem4n93r2t4JPQmmgcwUCZUDpDAIZAQAKCRD2t4JPQmmgcz33 EACjROM3nj9FGclR5AlyPUbAq/txEX7E0EFQCDtdLPrjBcLAoaYJIQUV8IDCcPjZMJy2ADp7 /zSwYba2rE2C9vRgjXZJNt21mySvKnnkPbNQGkNRl3TZAinO1Ddq3fp2c/GmYaW1NWFSfOmw MvB5CJaN0UK5l0/drnaA6Hxsu62V5UnpvxWgexqDuo0wfpEeP1PEqMNzyiVPvJ8bJxgM8qoC cpXLp1Rq/jq7pbUycY8GeYw2j+FVZJHlhL0w0Zm9CFHThHxRAm1tsIPc+oTorx7haXP+nN0J iqBXVAxLK2KxrHtMygim50xk2QpUotWYfZpRRv8dMygEPIB3f1Vi5JMwP4M47NZNdpqVkHrm jvcNuLfDgf/vqUvuXs2eA2/BkIHcOuAAbsvreX1WX1rTHmx5ud3OhsWQQRVL2rt+0p1DpROI 3Ob8F78W5rKr4HYvjX2Inpy3WahAm7FzUY184OyfPO/2zadKCqg8n01mWA9PXxs84bFEV2mP VzC5j6K8U3RNA6cb9bpE5bzXut6T2gxj6j+7TsgMQFhbyH/tZgpDjWvAiPZHb3sV29t8XaOF BwzqiI2AEkiWMySiHwCCMsIH9WUH7r7vpwROko89Tk+InpEbiphPjd7qAkyJ+tNIEWd1+MlX ZPtOaFLVHhLQ3PLFLkrU3+Yi3tXqpvLE3gO3LM7BTQRV4/npARAA5+u/Sx1n9anIqcgHpA7l 5SUCP1e/qF7n5DK8LiM10gYglgY0XHOBi0S7vHppH8hrtpizx+7t5DBdPJgVtR6SilyK0/mp 9nWHDhc9rwU3KmHYgFFsnX58eEmZxz2qsIY8juFor5r7kpcM5dRR9aB+HjlOOJJgyDxcJTwM 1ey4L/79P72wuXRhMibN14SX6TZzf+/XIOrM6TsULVJEIv1+NdczQbs6pBTpEK/G2apME7vf mjTsZU26Ezn+LDMX16lHTmIJi7Hlh7eifCGGM+g/AlDV6aWKFS+sBbwy+YoS0Zc3Yz8zrdbi Kzn3kbKd+99//mysSVsHaekQYyVvO0KD2KPKBs1S/ImrBb6XecqxGy/y/3HWHdngGEY2v2IP Qox7mAPznyKyXEfG+0rrVseZSEssKmY01IsgwwbmN9ZcqUKYNhjv67WMX7tNwiVbSrGLZoqf Xlgw4aAdnIMQyTW8nE6hH/Iwqay4S2str4HZtWwyWLitk7N+e+vxuK5qto4AxtB7VdimvKUs x6kQO5F3YWcC3vCXCgPwyV8133+fIR2L81R1L1q3swaEuh95vWj6iskxeNWSTyFAVKYYVskG V+OTtB71P1XCnb6AJCW9cKpC25+zxQqD2Zy0dK3u2RuKErajKBa/YWzuSaKAOkneFxG3LJIv Hl7iqPF+JDCjB5sAEQEAAcLBXwQYAQIACQUCVeP56QIbDAAKCRD2t4JPQmmgc5VnD/9YgbCr HR1FbMbm7td54UrYvZV/i7m3dIQNXK2e+Cbv5PXf19ce3XluaE+wA8D+vnIW5mbAAiojt3Mb 6p0WJS3QzbObzHNgAp3zy/L4lXwc6WW5vnpWAzqXFHP8D9PTpqvBALbXqL06smP47JqbyQxj Xf7D2rrPeIqbYmVY9da1KzMOVf3gReazYa89zZSdVkMojfWsbq05zwYU+SCWS3NiyF6QghbW voxbFwX1i/0xRwJiX9NNbRj1huVKQuS4W7rbWA87TrVQPXUAdkyd7FRYICNW+0gddysIwPoa KrLfx3Ba6Rpx0JznbrVOtXlihjl4KV8mtOPjYDY9u+8x412xXnlGl6AC4HLu2F3ECkamY4G6 UxejX+E6vW6Xe4n7H+rEX5UFgPRdYkS1TA/X3nMen9bouxNsvIJv7C6adZmMHqu/2azX7S7I vrxxySzOw9GxjoVTuzWMKWpDGP8n71IFeOot8JuPZtJ8omz+DZel+WCNZMVdVNLPOd5frqOv mpz0VhFAlNTjU1Vy0CnuxX3AM51J8dpdNyG0S8rADh6C8AKCDOfUstpq28/6oTaQv7QZdge0 JY6dglzGKnCi/zsmp2+1w559frz4+IC7j/igvJGX4KDDKUs0mlld8J2u2sBXv7CGxdzQoHaz lzVbFe7fduHbABmYz9cefQpO7wDE/Q== Organization: NGI0 Core In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Neal, On 24/07/2024 00:01, Neal Cardwell wrote: > On Tue, Jul 23, 2024 at 3:09 PM Matthieu Baerts wrote: >> >> Hi Eric, >> >> On 23/07/2024 18:42, Eric Dumazet wrote: >>> On Tue, Jul 23, 2024 at 6:08 PM Matthieu Baerts wrote: >>>> >>>> Hi Eric, >>>> >>>> On 23/07/2024 17:38, Eric Dumazet wrote: >>>>> On Tue, Jul 23, 2024 at 4:58 PM Matthieu Baerts wrote: >>>>>> >>>>>> Hi Eric, >>>>>> >>>>>> +cc Neal >>>>>> -cc Jerry (NoSuchUser) >>>>>> >>>>>> On 23/07/2024 16:37, Eric Dumazet wrote: >>>>>>> On Thu, Jul 18, 2024 at 12:34 PM Matthieu Baerts (NGI0) >>>>>>> wrote: >>>>>>>> > ... >>>>> +.045 < S. 1234:1234(0) ack 1001 win 14600 >>>> 940,nop,nop,sackOK,nop,wscale 6,FO 12345678,nop,nop> >>>>> +0 > . 1001:1001(0) ack 1 // See here >>>> >>>> I'm sorry, but is it normal to have 'ack 1' with 'sack 0:1' here? >>> >>> It is normal, because the SYN was already received/processed. >>> >>> sack 0:1 represents this SYN sequence. >> >> Thank you for your reply! >> >> Maybe it is just me, but does it not look strange to have the SACK >> covering a segment (0:1) that is before the ACK (1)? >> >> 'ack 1' and 'sack 0:1' seem to cover the same block, no? >> Before Kuniyuki's patch, this 'sack 0:1' was not present. > > A SACK that covers a sequence range that was already cumulatively or > selectively acknowledged is legal and useful, and is called a > Duplicate Selective Acknowledgement (DSACK or D-SACK). > > A DSACK indicates that a receiver received duplicate data. That can be > very useful in allowing a data sender to determine that a > retransmission was not needed (spurious). If a data sender receives > DSACKs for all retransmitted data in a loss detection episode then it > knows all retransmissions were spurious, and thus it can "undo" its > congestion control reaction to that estimated loss, since the > congestion control algorithm was responding to an incorrect loss > signal. This can be very helpful for performance in the presence of > varying delays or reordering, which can cause spurious loss detection > episodes.. > > See: > > https://datatracker.ietf.org/doc/html/rfc2883 > An Extension to the Selective Acknowledgement (SACK) Option for TCP > > https://www.rfc-editor.org/rfc/rfc3708.html > "Using TCP Duplicate Selective Acknowledgement (DSACKs) and Stream > Control Transmission Protocol (SCTP) Duplicate Transmission Sequence > Numbers (TSNs) to Detect Spurious Retransmissions" Thank you for the great explanations! I was not expecting this in a 3rd ACK :) I don't know if it will help the congestion control algorithm in this case, but I guess we don't need to worry about this marginal case. I will then send the v3, and the Packetdrill modification. Cheers, Matt -- Sponsored by the NGI0 Core fund.