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 3D65A224AE0 for ; Thu, 14 Aug 2025 11:47:17 +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=1755172040; cv=none; b=iwNT5qucIEJot6h8t9dK/3uR9lEokDn/7m6k8LsRRMWOa15ov+yttHpe1qyh2pRTWpA6M6wrP5KJgA4xoCrkwDBRqzTd00vBN12BJsOJWtG9qn1DBr5kYzHHlC+Kd8sgzq4xwgyx1GjV7wNbOsUUe84+itNoB839tpYeiAg42cY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755172040; c=relaxed/simple; bh=f9biXNrKh7+IcmUYdLBANnm43Z4mg6h9c78oLmSv8Mg=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=GMo7RNjVu5kP0qjf8QZemZHbmDXMRF11RTDOMIg/0PX5HQXfCE/R3WoTwwwfFSWnQq6JOiFKYYkNH2ne1z/6IsYlb3q6Jy/MxBWVXBqrkcyQ+lqJebRZAZ4nzYf+YHGjnKpbPnR5IVMRAHmjpba5+fdhrkCoL5LysOP78EckKCM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BvlVhefu; 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="BvlVhefu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7F16BC4CEED; Thu, 14 Aug 2025 11:47:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755172037; bh=f9biXNrKh7+IcmUYdLBANnm43Z4mg6h9c78oLmSv8Mg=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=BvlVhefuiE0yfezvRvoEL2JNUnCtE2ywWSvGS3AZLPQUvzuZCRt+GM1rAU1o0uah7 osT2A67pzkZ1aXoTLrCuGjkWgGfd/W7mZ6WgEeHqTR0O2WnuLU05/k4QyzbarmPIp+ 4DI8z7kGq+XxURu19yg6zoADdV0pCzZjEF1J0YGiI5ubgj5C66zoYp0k05lOMwkTgf 05Rwnr3+k0XQp80I3kRnArjoJEZmmwSlHVAChhZC23Cb0EEBYqvaWsSwN/7s1S/x5y /hN7iSUxrAXxbU/lo2Mgsn0rxZZ4zNq/OyUsckdEvah/0IoK2QjUD3v6T7w4MOASlH DcNC0TeurBUUQ== Message-ID: <3decc4cd-bbf1-45f1-9985-d2b795c5bfcc@kernel.org> Date: Thu, 14 Aug 2025 13:47:14 +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] mptcp: record subflows in RPS table Content-Language: en-GB, fr-BE From: Matthieu Baerts To: Christoph Paasch Cc: MPTCP Upstream , Geliang Tang , Mat Martineau References: <20250807-b4-mptcp_perf-v1-1-e89cc14179cc@openai.com> <2f037b38-c9f4-44a0-857c-0f65cbd50688@kernel.org> <4d933d54-fff1-4a9d-9601-753b8cddf934@kernel.org> 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: <4d933d54-fff1-4a9d-9601-753b8cddf934@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Christoph, On 14/08/2025 13:20, Matthieu Baerts wrote: > Hi Christoph, > > On 14/08/2025 05:31, Christoph Paasch wrote: >> On Wed, Aug 13, 2025 at 7:54 AM Matthieu Baerts wrote: >>> >>> Hi Christoph, >>> >>> On 07/08/2025 20:14, Christoph Paasch via B4 Relay wrote: >>>> From: Christoph Paasch >>>> >>>> Accelerated Receive Flow Steering (aRFS) relies on sockets recording >>>> their RX flow hash into the rps_sock_flow_table so that incoming packets >>>> are steered to the CPU where the application runs. >>>> >>>> With MPTCP, the application interacts with the parent MPTCP socket while >>>> data is carried over per-subflow TCP sockets. Without recording these >>>> subflows, aRFS cannot steer interrupts and RX processing for the flows >>>> to the desired CPU. >>>> >>>> Record all subflows in the RPS table by calling sock_rps_record_flow() >>>> for each subflow at the start of mptcp_sendmsg() and mptcp_recvmsg(). >>>> >>>> It does not by itself improve throughput, but ensures that IRQ and RX >>>> processing are directed to the right CPU, which is a >>>> prerequisite for effective aRFS. >>> >>> Thank you for looking at that! >>> >>>> Signed-off-by: Christoph Paasch >>>> --- >>>> net/mptcp/protocol.c | 16 ++++++++++++++++ >>>> 1 file changed, 16 insertions(+) >>>> >>>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c >>>> index 4b510e04724f5c8be08a00a1cc03093bcd031905..86f1fc5be47bd5f6dc8bf40a488de32f253c1beb 100644 >>>> --- a/net/mptcp/protocol.c >>>> +++ b/net/mptcp/protocol.c >>>> @@ -12,6 +12,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> #include >>>> #include >>>> #include >>>> @@ -1740,6 +1741,17 @@ static u32 mptcp_send_limit(const struct sock *sk) >>>> return limit - not_sent; >>>> } >>>> >>>> +static void mptcp_rps_record_subflows(const struct mptcp_sock *msk) >>>> +{ >>>> + struct mptcp_subflow_context *subflow; >>>> + >>>> + mptcp_for_each_subflow(msk, subflow) { >>>> + struct sock *ssk = mptcp_subflow_tcp_sock(subflow); >>>> + >>>> + sock_rps_record_flow(ssk); >>> >>> Should we eventually open code this RPS function and directly call >>> sock_rps_record_flow_hash()? If RPS is not needed, no need to go through >>> the subflow list. So we could add: #ifdef CONFIG_RPS + &rfs_needed >>> before the for_each, then check the state for each subflow, no? >>> >>> Or maybe such optimisation is not worth it? >> >> IMO it's not worth it. Because it would also mean that we pull in more >> of non-MPTCP things over to MPTCP files. > > Good point for the maintenance! > > But then, what about adding a small helper in include/net/rps.h? Here we > could have this at the top of mptcp_rps_record_subflows(): > > if (!sock_rps_record_needed()) /* with likely()? */ > return; > > I'm suggesting this because rfs is disabled by default, so it sounds > better to check that before iterating over different subflows for > nothing, no? > >>> While at it, I see that sock_rps_record_flow() is called in >>> __inet_accept(), inet(6)_sendmsg and inet(6)_recvmsg, but with the msk. >>> I guess that's OK, right? >> >> AFAICS, that should be alright. sk_rxhash should not be set on an msk. >> Even on the passive opener side, we clone msk from the ssk, but at >> that point sk_rxhash is not set yet. (I may be wrong of course, I'm >> still not super familiar with the source-code...) > > Thank you for having looked! I guess you would have seen issues when > testing if there was a problem with that, so no need to investigate more. > >>> Also, is sock_rps_record_flow() called when a subflow is "accept()ed", >>> or is there something else to do there for this subflow to copy TCP's >>> behaviour? >> >> For new subflows, I don't think we can easily do that. Because >> sock_rps_record_flow() records the CPU on which it is running. From >> what I see, when new subflows get accepted, that is not happening in >> the application's context necessarily. So, we have to wait for a >> recvmsg/sendmsg. > > Ah yes, of course, we should not do it there for additional subflows! > And for the first subflow, I think that it will be done because when an > accept() is triggered from the userspace, mptcp_stream_accept(msk, arg) > will call inet_csk_accept(ssk, arg) that will end up doing that I think. My bad, I think __inet_accept will not be called from inet_csk_accept(). For TCP, I think the path is: inet_accept() --> inet_csk_accept() --> __inet_accept() But with MPTCP, mptcp_stream_accept is called instead of inet_accept(), and I don't think __inet_accept() will be called on a subflow. (I didn't validate that.) Then, maybe we should call sock_rps_record_flow() on the newsk in mptcp_stream_accept, no? Cheers, Matt -- Sponsored by the NGI0 Core fund.