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 2FC7636606C; Wed, 4 Mar 2026 18:09:20 +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=1772647761; cv=none; b=nym73tRj5iqnzGE0/pOt2mmsrFkREQijUXOlw1ZxpOAGRFu25WLksPlzI0UV8bYR3iIf9GPwSLWicaVx1FXn4ympZyUn5nCacJuMKjYUY4Jt4T3+CnXhDv4r1KG+eVoYwcze/J1cm2/RaewI8g5hcRvxCkvGWOupJ3UmJob3N+c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772647761; c=relaxed/simple; bh=7jQRA3snqnsf4BSfmZNNQ1jfm/rYYIIAXy8ZKrX178M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=j1NRQCGBPyKwz4LTQdtvp0zcpteA6xz4Hh/d2FOOY8hvKmROY9MHItwgOEv9QqqWY59wuMT05m1DZkjnDMAanh+8wGEnGy6K5zFIbVES5XsVUX+xv4Qo5qqOV+9wH34/KMx5mnHG+Ock9gpR0cKlYTGDdKUMVGsNg3Ssw6Dc1OA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Kui/BTgP; 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="Kui/BTgP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78CD7C4CEF7; Wed, 4 Mar 2026 18:09:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772647760; bh=7jQRA3snqnsf4BSfmZNNQ1jfm/rYYIIAXy8ZKrX178M=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Kui/BTgPjcqnx70pbVUMW77ToLmspZPrdzk9ONOVu1WBnNhIpbfBGsy58tvfbovbj HUPTSMaqjMSmND05jZM9gK8HA1nhiRuz1LgNY+g+6tm2xdLTx+CykPiiKmI+ZhsJTT Gn0Ms7lEMv+D4OcgSLUJQKJJrcz8lgBz56L+qydJeYMbbdTMmqZngv02Cnlgb6SZ7E n6DD+2q1JH2g3K/SWm9ZkYNB1Db5yIjTHTlZsrDRFuzkQN9SYB1muZA4G9HzpbrHeL 5MYQW7xb+WchwgUa3NGnp113CHqEDkD57ILFpDx699pEalcgPPsLHDTlw4BxtldfcS MHz2AR0EPxmsw== Message-ID: <072854a1-0521-40ef-b963-6e3e56084281@kernel.org> Date: Wed, 4 Mar 2026 19:09:12 +0100 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-next V2 RESEND] tcp: shrink per-packet memset in __tcp_transmit_skb() To: Keita Morisaki Cc: Kuniyuki Iwashima , Simon Horman , Jakub Sitnicki , Mat Martineau , Geliang Tang , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, mptcp@lists.linux.dev, Eric Dumazet , Neal Cardwell , "David S . Miller" , David Ahern , Jakub Kicinski , Paolo Abeni References: <20260304111517.2088694-1-kmta1236@gmail.com> From: Matthieu Baerts Content-Language: en-GB, fr-BE 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: <20260304111517.2088694-1-kmta1236@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Keita, On 04/03/2026 12:15, Keita Morisaki wrote: > Use struct_group() to group the three fields in tcp_out_options that are > read unconditionally by tcp_options_write() and bpf_skops_write_hdr_opt() > (mss, bpf_opt_len, num_sack_blocks), then replace the full-struct memset > with a targeted memset of only that group. > > struct tcp_out_options is 40 bytes without MPTCP and 96 bytes with > CONFIG_MPTCP=y (typical distro config). Every remaining field is either > assigned before first use by tcp_established_options()/tcp_syn_options(), > or gated behind its OPTION_* flag in tcp_options_write(). This memset > runs on every transmitted TCP packet, so shrinking it from 96 (or 40) > bytes to 4 bytes reduces per-packet overhead on the hot path. > > Assembly comparison (x86-64, GCC 13, CONFIG_MPTCP=y): > > Before: rep stos zeroing 96 bytes (5 instructions, 12 8-byte stores) > After: movl $0x0 zeroing 4 bytes (1 instruction, 1 store) > > Also add opts->options = 0 at the top of tcp_syn_options(), which > already used |= without a prior clear. tcp_established_options() already > clears opts->options at its top. Thank you for this patch! It looks good to me: Acked-by: Matthieu Baerts (NGI0) Cheers, Matt -- Sponsored by the NGI0 Core fund.