Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751776AbbEZUUN (ORCPT ); Tue, 26 May 2015 16:20:13 -0400 Received: from mail-qk0-f171.google.com ([209.85.220.171]:35220 "EHLO mail-qk0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751282AbbEZUUL (ORCPT ); Tue, 26 May 2015 16:20:11 -0400 From: Ido Yariv To: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , Nandita Dukkipati , Eric Dumazet , 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 16:17:17 -0400 Message-Id: <1432671437-19140-1-git-send-email-ido@wizery.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1432663992.4060.286.camel@edumazet-glaptop2.roam.corp.google.com> References: <1432663992.4060.286.camel@edumazet-glaptop2.roam.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1414 Lines: 41 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 may expire prematurely. This is especially problematic on systems in which HZ <= 100, so work around this by setting the timeout to at least 2 jiffies on such systems. The 10ms figure was originally selected based on tests performed with the current implementation and HZ = 1000. Thus, leave the behavior on systems with HZ > 100 unchanged. Signed-off-by: Ido Yariv --- net/ipv4/tcp_output.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 534e5fd..5321df8 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2208,6 +2208,9 @@ bool tcp_schedule_loss_probe(struct sock *sk) timeout = max_t(u32, timeout, (rtt + (rtt >> 1) + TCP_DELACK_MAX)); timeout = max_t(u32, timeout, msecs_to_jiffies(10)); +#if HZ <= 100 + timeout = max_t(u32, timeout, 2); +#endif /* 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/