Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752068AbbEZO0W (ORCPT ); Tue, 26 May 2015 10:26:22 -0400 Received: from mail-qg0-f53.google.com ([209.85.192.53]:35244 "EHLO mail-qg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751358AbbEZO0S (ORCPT ); Tue, 26 May 2015 10:26:18 -0400 From: Ido Yariv To: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , Nandita Dukkipati , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Ido Yariv , Ido Yariv Subject: [PATCH] net: tcp: Fix a PTO timing granularity issue Date: Tue, 26 May 2015 10:25:58 -0400 Message-Id: <1432650358-11470-1-git-send-email-ido@wizery.com> X-Mailer: git-send-email 2.1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1322 Lines: 35 The Tail Loss Probe RFC specifies that the PTO value should be set to max(2 * SRTT, 10ms), where SRTT is the smoothed round-trip time. The PTO value is converted to jiffies, so the timer might expire prematurely. This is especially problematic on systems in which HZ=100. To work around this issue, increase the number of jiffies by one, ensuring that the timeout won't expire in less than 10ms. Signed-off-by: Ido Yariv --- net/ipv4/tcp_output.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 534e5fd..6f57d3d 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2207,7 +2207,7 @@ bool tcp_schedule_loss_probe(struct sock *sk) if (tp->packets_out == 1) timeout = max_t(u32, timeout, (rtt + (rtt >> 1) + TCP_DELACK_MAX)); - timeout = max_t(u32, timeout, msecs_to_jiffies(10)); + timeout = max_t(u32, timeout, msecs_to_jiffies(10) + 1); /* If RTO is shorter, just schedule TLP in its place. */ tlp_time_stamp = tcp_time_stamp + timeout; -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/