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 65F652DC78C; Tue, 11 Nov 2025 01:14:50 +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=1762823690; cv=none; b=ljQZer581n6U/e3Yw8FIqWWA72ieAjbM/s/hSUUoG8E+uLG0j2vi7wbU50aMuKtnV6OkAStL1XjKq3uHx3A9UMmMQwtEtE0cADV4j8cm88D53q3jSXHGXCznmU3QkbwAsSy7vJ2ItW70bYz89Z1UVI7liX5R1Cf1IpIOLaRyg48= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762823690; c=relaxed/simple; bh=AJZ3/qPZk3jVdaks5zN3LXcgA68wf/zudXv3m4o6LNg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LhqTmgeagT+PvrbBqsA9h+Y0wzesfPQzHo5Z/ZErk64OgzspyVvIhZcF5OlRL3OnJK45ulr6zPpiJRJQ/WEFwk8sN03QPchq7lDB4JvSAyXFELSSY0pqyGdlWzUQ0rkwRoaa1JuCE+KtSkFnt00p+zqi+8n3+aJf0IPxEH/clTk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=UZIGzCn6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="UZIGzCn6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 04BA0C16AAE; Tue, 11 Nov 2025 01:14:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1762823690; bh=AJZ3/qPZk3jVdaks5zN3LXcgA68wf/zudXv3m4o6LNg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UZIGzCn6rIiUZUzdfliTHKm001C6PI0qgJJ14qHNLhzyxoEgnK+vd5wLLhCerPyeU +o8YoF3PTwoPx/y+uQHd/4lrTo+9lZx5+O5sgYDXk0295hWYnrHCu58luDtlNonGTV LZNrSbdl07ihrPZduuaBB+VC2miLAVnIDoviFeeA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Eric Dumazet , Kuniyuki Iwashima , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.12 301/565] net: call cond_resched() less often in __release_sock() Date: Tue, 11 Nov 2025 09:42:37 +0900 Message-ID: <20251111004533.649912675@linuxfoundation.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251111004526.816196597@linuxfoundation.org> References: <20251111004526.816196597@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 16c610162d1f1c332209de1c91ffb09b659bb65d ] While stress testing TCP I had unexpected retransmits and sack packets when a single cpu receives data from multiple high-throughput flows. super_netperf 4 -H srv -T,10 -l 3000 & Tcpdump extract: 00:00:00.000007 IP6 clnt > srv: Flags [.], seq 26062848:26124288, ack 1, win 66, options [nop,nop,TS val 651460834 ecr 3100749131], length 61440 00:00:00.000006 IP6 clnt > srv: Flags [.], seq 26124288:26185728, ack 1, win 66, options [nop,nop,TS val 651460834 ecr 3100749131], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [P.], seq 26185728:26243072, ack 1, win 66, options [nop,nop,TS val 651460834 ecr 3100749131], length 57344 00:00:00.000006 IP6 clnt > srv: Flags [.], seq 26243072:26304512, ack 1, win 66, options [nop,nop,TS val 651460844 ecr 3100749141], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [.], seq 26304512:26365952, ack 1, win 66, options [nop,nop,TS val 651460844 ecr 3100749141], length 61440 00:00:00.000007 IP6 clnt > srv: Flags [P.], seq 26365952:26423296, ack 1, win 66, options [nop,nop,TS val 651460844 ecr 3100749141], length 57344 00:00:00.000006 IP6 clnt > srv: Flags [.], seq 26423296:26484736, ack 1, win 66, options [nop,nop,TS val 651460853 ecr 3100749150], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [.], seq 26484736:26546176, ack 1, win 66, options [nop,nop,TS val 651460853 ecr 3100749150], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [P.], seq 26546176:26603520, ack 1, win 66, options [nop,nop,TS val 651460853 ecr 3100749150], length 57344 00:00:00.003932 IP6 clnt > srv: Flags [P.], seq 26603520:26619904, ack 1, win 66, options [nop,nop,TS val 651464844 ecr 3100753141], length 16384 00:00:00.006602 IP6 clnt > srv: Flags [.], seq 24862720:24866816, ack 1, win 66, options [nop,nop,TS val 651471419 ecr 3100759716], length 4096 00:00:00.013000 IP6 clnt > srv: Flags [.], seq 24862720:24866816, ack 1, win 66, options [nop,nop,TS val 651484421 ecr 3100772718], length 4096 00:00:00.000416 IP6 srv > clnt: Flags [.], ack 26619904, win 1393, options [nop,nop,TS val 3100773185 ecr 651484421,nop,nop,sack 1 {24862720:24866816}], length 0 After analysis, it appears this is because of the cond_resched() call from __release_sock(). When current thread is yielding, while still holding the TCP socket lock, it might regain the cpu after a very long time. Other peer TLP/RTO is firing (multiple times) and packets are retransmit, while the initial copy is waiting in the socket backlog or receive queue. In this patch, I call cond_resched() only once every 16 packets. Modern TCP stack now spends less time per packet in the backlog, especially because ACK are no longer sent (commit 133c4c0d3717 "tcp: defer regular ACK while processing socket backlog") Before: clnt:/# nstat -n;sleep 10;nstat|egrep "TcpOutSegs|TcpRetransSegs|TCPFastRetrans|TCPTimeouts|Probes|TCPSpuriousRTOs|DSACK" TcpOutSegs 19046186 0.0 TcpRetransSegs 1471 0.0 TcpExtTCPTimeouts 1397 0.0 TcpExtTCPLossProbes 1356 0.0 TcpExtTCPDSACKRecv 1352 0.0 TcpExtTCPSpuriousRTOs 114 0.0 TcpExtTCPDSACKRecvSegs 1352 0.0 After: clnt:/# nstat -n;sleep 10;nstat|egrep "TcpOutSegs|TcpRetransSegs|TCPFastRetrans|TCPTimeouts|Probes|TCPSpuriousRTOs|DSACK" TcpOutSegs 19218936 0.0 Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250903174811.1930820-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/core/sock.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/net/core/sock.c b/net/core/sock.c index bf31b19045243..1781f3a642b46 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3093,23 +3093,27 @@ void __release_sock(struct sock *sk) __acquires(&sk->sk_lock.slock) { struct sk_buff *skb, *next; + int nb = 0; while ((skb = sk->sk_backlog.head) != NULL) { sk->sk_backlog.head = sk->sk_backlog.tail = NULL; spin_unlock_bh(&sk->sk_lock.slock); - do { + while (1) { next = skb->next; prefetch(next); DEBUG_NET_WARN_ON_ONCE(skb_dst_is_noref(skb)); skb_mark_not_on_list(skb); sk_backlog_rcv(sk, skb); - cond_resched(); - skb = next; - } while (skb != NULL); + if (!skb) + break; + + if (!(++nb & 15)) + cond_resched(); + } spin_lock_bh(&sk->sk_lock.slock); } -- 2.51.0