From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=GQGyyJIq; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by passt.top (Postfix) with ESMTPS id 943A95A0620 for ; Tue, 14 Oct 2025 09:39:01 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760427540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/ikvVkR5XvBfVmS/LDJKwLQ4xSg68yFjCoGUjkgsIqU=; b=GQGyyJIqFI22hgMmR2ryNsQcLTAxo3/CetATv9EyELQke7t5K1JWSJ/e5e4fblbkxn3T+0 5TxI/YP/av6EV74E218pEdr+GqM4v48jFbOWOWzKwd5aYnwhIuNTH78RLYcCfmO2N8w9xf Xgn6fWhdOd1ajW+RTk5+v5bPcK60XIM= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-616-mZNTMwBMM8W89bs1XC450w-1; Tue, 14 Oct 2025 03:38:59 -0400 X-MC-Unique: mZNTMwBMM8W89bs1XC450w-1 X-Mimecast-MFC-AGG-ID: mZNTMwBMM8W89bs1XC450w_1760427538 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 46CD019560AD; Tue, 14 Oct 2025 07:38:58 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.72.112.76]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id E08C4300018D; Tue, 14 Oct 2025 07:38:55 +0000 (UTC) From: Yumei Huang To: passt-dev@passt.top, sbrivio@redhat.com Subject: [PATCH v3 4/4] tcp: Update data retransmission timeout Date: Tue, 14 Oct 2025 15:38:36 +0800 Message-ID: <20251014073836.18150-5-yuhuang@redhat.com> In-Reply-To: <20251014073836.18150-1-yuhuang@redhat.com> References: <20251014073836.18150-1-yuhuang@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 3YPl-RrNGbXs7NO0CcWJ4dP_C62p44S-tCvFS6GQHSc_1760427538 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Message-ID-Hash: 55VTYHHGMY7HWKGT3KN2BJB77F5U3X2O X-Message-ID-Hash: 55VTYHHGMY7HWKGT3KN2BJB77F5U3X2O X-MailFrom: yuhuang@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: david@gibson.dropbear.id.au, yuhuang@redhat.com X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: According to RFC 2988 and RFC 6298, we should use an exponential backoff timeout for data retransmission starting from one second (see Appendix A in RFC 6298), and limit it to about 60 seconds as allowed by the same RFC: (2.5) A maximum value MAY be placed on RTO provided it is at least 60 seconds. Combine the macros defining the initial timeout for both SYN and ACK. And add a macro ACK_RETRIES to limit the total timeout to about 60s. Signed-off-by: Yumei Huang --- tcp.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) diff --git a/tcp.c b/tcp.c index 3ce3991..84da069 100644 --- a/tcp.c +++ b/tcp.c @@ -179,16 +179,12 @@ * * Timeouts are implemented by means of timerfd timers, set based on flags: * - * - SYN_TIMEOUT_INIT: if no ACK is received from tap/guest during handshake - * (flag ACK_FROM_TAP_DUE without ESTABLISHED event) within this time, resend - * SYN. It's the starting timeout for the first SYN retry. If this persists - * for more than TCP_MAX_RETRIES or (tcp_syn_retries + - * tcp_syn_linear_timeouts) times in a row, reset the connection - * - * - ACK_TIMEOUT: if no ACK segment was received from tap/guest, after sending - * data (flag ACK_FROM_TAP_DUE with ESTABLISHED event), re-send data from the - * socket and reset sequence to what was acknowledged. If this persists for - * more than TCP_MAX_RETRIES times in a row, reset the connection + * - ACK_TIMEOUT_INIT: if no ACK segment was received from tap/guest, eiher + * during handshake(flag ACK_FROM_TAP_DUE without ESTABLISHED event) or after + * sending data (flag ACK_FROM_TAP_DUE with ESTABLISHED event), re-send data + * from the socket and reset sequence to what was acknowledged. It's the + * starting timeout for the first retry. If this persists for more than + * allowed times in a row, reset the connection * * - FIN_TIMEOUT: if a FIN segment was sent to tap/guest (flag ACK_FROM_TAP_DUE * with TAP_FIN_SENT event), and no ACK is received within this time, reset @@ -342,8 +338,7 @@ enum { #define WINDOW_DEFAULT 14600 /* RFC 6928 */ #define ACK_INTERVAL 10 /* ms */ -#define SYN_TIMEOUT_INIT 1 /* s */ -#define ACK_TIMEOUT 2 +#define ACK_TIMEOUT_INIT 1 /* s, RFC 6298 */ #define FIN_TIMEOUT 60 #define ACT_TIMEOUT 7200 @@ -352,6 +347,11 @@ enum { #define ACK_IF_NEEDED 0 /* See tcp_send_flag() */ +/* Number of retries calculated from the exponential backoff formula, limited + * by a total timeout of about 60 seconds. + */ +#define ACK_RETRIES 5 + #define CONN_IS_CLOSING(conn) \ (((conn)->events & ESTABLISHED) && \ ((conn)->events & (SOCK_FIN_RCVD | TAP_FIN_RCVD))) @@ -589,13 +589,13 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn) } else if (conn->flags & ACK_FROM_TAP_DUE) { if (!(conn->events & ESTABLISHED)) { if (conn->retries < c->tcp.syn_linear_timeouts) - it.it_value.tv_sec = SYN_TIMEOUT_INIT; + it.it_value.tv_sec = ACK_TIMEOUT_INIT; else - it.it_value.tv_sec = SYN_TIMEOUT_INIT << + it.it_value.tv_sec = ACK_TIMEOUT_INIT << (conn->retries - c->tcp.syn_linear_timeouts); } else - it.it_value.tv_sec = ACK_TIMEOUT; + it.it_value.tv_sec = ACK_TIMEOUT_INIT << conn->retries; } else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) { it.it_value.tv_sec = FIN_TIMEOUT; } else { @@ -2433,7 +2433,7 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref) } else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) { flow_dbg(conn, "FIN timeout"); tcp_rst(c, conn); - } else if (conn->retries == TCP_MAX_RETRIES) { + } else if (conn->retries >= ACK_RETRIES) { flow_dbg(conn, "retransmissions count exceeded"); tcp_rst(c, conn); } else { -- 2.47.0