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 7168A246BDE for ; Thu, 23 Oct 2025 15:52:22 +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=1761234742; cv=none; b=WKMZD3HaMDnO2qPtJtPovY/EidFLpxBKPNj2lO2W/EDozlvLPRgcNWFlqYrJyTBDF9yiHBqECjr59z/ojLRjMjW/FEXOsRjx/DQULKLFMLIsOoGdnwGiyQwRzUjS1dt5y/p0n7KH2vRhxL80rBRUGHwFftvJY1RSeg4Etr3vOog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761234742; c=relaxed/simple; bh=oHIK9b3ZEPl2lvLKKsRkoeYK/U3y2hjpW9NuIZhjqpU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Mkp5U/R5MMOrr8QYwfiIfmWGo84bTXhbQ+jn6kgyb5avrbcZsCLM4nldF6+VujTFh655O40q7/6hiGLAUfEgv8sCJXFdKMuZbpJcBI4bARGYuc/0RhST8r2TewqYaOOxOkmlbbSRQTIZsuAUlwtQi4YC1yLfsq5NkUe7SwJ8e6A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kD9Vwl6C; 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="kD9Vwl6C" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D74EBC16AAE; Thu, 23 Oct 2025 15:52:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761234742; bh=oHIK9b3ZEPl2lvLKKsRkoeYK/U3y2hjpW9NuIZhjqpU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=kD9Vwl6CyuvvG3zXBHxwFiu5GRX5yVQqbTGCKo4XQ4Ms9VEgfg1l4CDxgruSRoeAt aAJF6s2T++jgB8Fr1i+RLvnewUJ30WTIY0AmP0vmZp2lC02WfkxtYqJOEjwVlc6gc+ GB+nKj2uxSDMhBJNSBj6jHty8Ik5lQelldgdpPNngRVBKYaLw5njgvsVtS68UhuM3y g7Z8NkBRnmag9tNP6C4sSBripV77idlBOQY9Qhq58pT1pEDSryogVtmyVmD9LGntOP PJPfb4I3RA+FCiz/ZqLZ4MQ/6KSIdtiQ+UYMCvWQZZ0Bsf6nrGGTOEKsoOGfATrI4w pAQF8YYnAA3Iw== Message-ID: <34f90baa-72ff-4c00-917a-a0d65ff0e608@kernel.org> Date: Thu, 23 Oct 2025 17:52:18 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 mptcp-next 11/11] mptcp: leverage the backlog for RX packet processing Content-Language: en-GB, fr-BE To: Paolo Abeni , Mat Martineau Cc: Geliang Tang , mptcp@lists.linux.dev References: <2201f259d2176bca0ad37500a352658f7ef5a1f0.1761142784.git.pabeni@redhat.com> <3feb8c2a-2098-4626-8bf2-edd66f679463@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, Mat, On 23/10/2025 17:11, Paolo Abeni wrote: > > > On 10/22/25 4:31 PM, Paolo Abeni wrote: >> When the msk socket is owned or the msk receive buffer is full, >> move the incoming skbs in a msk level backlog list. This avoid >> traversing the joined subflows and acquiring the subflow level >> socket lock at reception time, improving the RX performances. >> >> When processing the backlog, use the fwd alloc memory borrowed from >> the incoming subflow. skbs exceeding the msk receive space are >> not dropped; instead they are kept into the backlog until the receive >> buffer is freed. Dropping packets already acked at the TCP level is >> explicitly discouraged by the RFC and would corrupt the data stream >> for fallback sockets. >> >> Move the conditional reschedule in release_cb() to take action only >> after the first loop iteration, to avoid rescheduling just before >> releasing the lock. >> >> Special care is needed to avoid adding skbs to the backlog of a closed >> msk and to avoid leaving dangling references into the backlog >> at subflow closing time. (...) >> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c >> index 5a1d8f9e0fb0ec..0aae17ab77edb2 100644 >> --- a/net/mptcp/protocol.c >> +++ b/net/mptcp/protocol.c (...) >> -static bool __mptcp_move_skbs(struct sock *sk) >> +static bool mptcp_can_spool_backlog(struct sock *sk, u32 moved, >> + struct list_head *skbs) >> { >> - struct mptcp_subflow_context *subflow; >> struct mptcp_sock *msk = mptcp_sk(sk); >> - bool ret = false; >> >> - if (list_empty(&msk->conn_list)) >> + if (list_empty(&msk->backlog_list)) >> return false; >> >> - subflow = list_first_entry(&msk->conn_list, >> - struct mptcp_subflow_context, node); >> - for (;;) { >> - struct sock *ssk; >> - bool slowpath; >> + /* Borrowed mem could be zero only in the unlikely event that the bl >> + * is full >> + */ >> + if (likely(msk->borrowed_mem)) { >> + sk_forward_alloc_add(sk, msk->borrowed_mem); >> + msk->borrowed_mem = 0; >> + sk->sk_reserved_mem = msk->backlog_len; > > With the above I intended to prevent the fwd memory handling from > releasing backlog_len bytes. Re-reading the relevant code, it does not > allow that (experimentation confirmed), see: > > https://elixir.bootlin.com/linux/v6.18-rc2/source/include/net/sock.h#L1593 > > and: > > https://elixir.bootlin.com/linux/v6.18-rc2/source/include/net/sock.h#L1580 > > This will need some more care. Also patch 2 will require some > significant rework. Thank you for looking at this complex part, and for having spot that! > @Mat, @Matttbe: could you please consider merging patches 1,3-9? > > I think they should be pretty uncontroversial, would make the series > more manegeable for future iterations (and would alleviate my > frustration to make this thing work correctly). It makes sense, fine by me. I will wait for Mat's review before applying them (patch 1 is for 'net' I suppose). Cheers, Matt -- Sponsored by the NGI0 Core fund.