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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZMrveFIO; 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="ZMrveFIO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BE9B6C4CEEB; Thu, 7 Aug 2025 11:56:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754567805; bh=QbAP06Gg2mJ3cgaybBL3Iz7qhvNWWd253kNdvLtY7FE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZMrveFIO7lPRfO6mBBQhwDz4EmoPAri/64RQLBxLTomq5cfQgpWvAXhqzAw7U8Vbq Uzfam9GHzIIiJHRRGIOBwp97lI/AAvg11sH0OVNi6C7nd+h/JerC290l9rjXjXpqlp /q3w3zG13aOmzdWxGFNHxQkEYfTJl/r4/6TiTtknElHWu4C4cmYlhmwpWrdBV8gMRr 88S1U54LdVfpNWobolkn8ermNEgvcW3weDlrpuSWZK8s67LUyfId11c8N+2Cja4uSM JwwJ9wdA+XJhTcJA9SIpDoVM9H40bANw3JdRQIpR8SeK207JudRV8PNJbq4pGo1EIe 3Dh+4LGU5gKvg== Message-ID: Date: Thu, 7 Aug 2025 13:56:41 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-next v3 2/3] mptcp: make ADD_ADDR retransmission timeout adaptive Content-Language: en-GB, fr-BE To: Geliang Tang , mptcp@lists.linux.dev Cc: Geliang Tang , Christoph Paasch References: From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, On 07/08/2025 05:25, Geliang Tang wrote: > Hi Matt, > > On Wed, 2025-08-06 at 17:34 +0200, Matthieu Baerts wrote: >> Hi Geliang, >> >> On 06/08/2025 05:17, Geliang Tang wrote: >>> From: Geliang Tang >>> >>> Replace the fixed ADD_ADDR retransmission timeout with an adaptive >>> mechanism that uses the maximum RTO among existing subflows. This >>> improves responsiveness when establishing new subflows while >>> maintaining >>> an upper bound through the configured add_addr_timeout value. >>> >>> Key changes: >>> 1. Compute timeout as min(max_subflow_RTO, configured_max_timeout) >>> 2. Apply exponential backoff based on retransmission count >>> 3. Maintain fallback to configured max timeout when no subflows >>> exist >>> 4. Update documentation to clarify add_addr_timeout is now the >>> maximum >>> value >>> >>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/576 >>> Reviewed-by: Christoph Paasch >>> Signed-off-by: Geliang Tang >>> --- >>>  Documentation/networking/mptcp-sysctl.rst |  4 +-- >>>  net/mptcp/pm.c                            | 30 >>> ++++++++++++++++++++--- >>>  2 files changed, 29 insertions(+), 5 deletions(-) >>> >>> diff --git a/Documentation/networking/mptcp-sysctl.rst >>> b/Documentation/networking/mptcp-sysctl.rst >>> index 1683c139821e..2b8e8fb99ee2 100644 >>> --- a/Documentation/networking/mptcp-sysctl.rst >>> +++ b/Documentation/networking/mptcp-sysctl.rst >>> @@ -8,8 +8,8 @@ MPTCP Sysfs variables >>>  =============================== >>>   >>>  add_addr_timeout - INTEGER (seconds) >>> - Set the timeout after which an ADD_ADDR control message >>> will be >>> - resent to an MPTCP peer that has not acknowledged a >>> previous >>> + Set the maximum value of timeout after which an ADD_ADDR >>> control message >>> + will be resent to an MPTCP peer that has not acknowledged >>> a previous >>>   ADD_ADDR message. >>>   >>>   Do not retransmit if set to 0. >>> diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c >>> index 1330af6a2154..34cc4f45bc7d 100644 >>> --- a/net/mptcp/pm.c >>> +++ b/net/mptcp/pm.c >>> @@ -268,6 +268,30 @@ int mptcp_pm_mp_prio_send_ack(struct >>> mptcp_sock *msk, >>>   return -EINVAL; >>>  } >>>   >>> +static unsigned int mptcp_adjust_add_addr_timeout(struct >>> mptcp_sock *msk) >>> +{ >>> + struct mptcp_subflow_context *subflow; >>> + struct sock *sk = (struct sock *)msk; >>> + unsigned int max_rto = 0; >>> + unsigned int timeout; >>> + >>> + timeout = mptcp_get_add_addr_timeout(sock_net(sk)); >>> + >>> + mptcp_for_each_subflow(msk, subflow) { >>> + struct sock *ssk = >>> mptcp_subflow_tcp_sock(subflow); >>> + unsigned int subflow_rto; >>> + >>> + subflow_rto = __tcp_set_rto(tcp_sk(ssk)) * 2; >> >> Why "* 2"? Is it what TCP is doing? >> >> (Probably best to add a comment here above, and in the commit >> message.) >> >> (Also, I guess the compiler will do the optimisation, but you could >> write: ">> 1" instead of "* 2". > > Yes, "<< 1" is much better. I added a comment here: > > + /* > + * icsk->icsk_rto is not used directly since > + * it's not updated frequently enough. > + * > + * subflow_rto is twice of rto, and allow > + * some tolerance for add_addr echo. > + */ > + subflow_rto = __tcp_set_rto(tcp_sk(ssk)) << 1; > > Is this okay? No :) I don't think the comment explain why it is twice the default TCP RTO. Why having an exception here for the ADD_ADDR? I mean: I'm OK with the idea of doubling the RTO, but only if there is a reason behind that :) Cheers, Matt -- Sponsored by the NGI0 Core fund.