From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neal Cardwell Subject: [PATCH net 2/3] tcp: enable xmit timer fix by having TLP use time when RTO should fire Date: Mon, 31 Jul 2017 22:58:13 -0400 Message-ID: <20170801025814.31206-3-ncardwell@google.com> References: <20170801025814.31206-1-ncardwell@google.com> Cc: netdev@vger.kernel.org, Neal Cardwell , Yuchung Cheng , Nandita Dukkipati To: David Miller Return-path: Received: from mail-qt0-f180.google.com ([209.85.216.180]:35746 "EHLO mail-qt0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751725AbdHAC6l (ORCPT ); Mon, 31 Jul 2017 22:58:41 -0400 Received: by mail-qt0-f180.google.com with SMTP id p3so2154501qtg.2 for ; Mon, 31 Jul 2017 19:58:41 -0700 (PDT) In-Reply-To: <20170801025814.31206-1-ncardwell@google.com> Sender: netdev-owner@vger.kernel.org List-ID: Have tcp_schedule_loss_probe() base the TLP scheduling decision based on when the RTO *should* fire. This is to enable the upcoming xmit timer fix in this series, where tcp_schedule_loss_probe() cannot assume that the last timer installed was an RTO timer (because we are no longer doing the "rearm RTO, rearm RTO, rearm TLP" dance on every ACK). So tcp_schedule_loss_probe() must independently figure out when an RTO would want to fire. In the new TLP implementation following in this series, we cannot assume that icsk_timeout was set based on an RTO; after processing a cumulative ACK the icsk_timeout we see can be from a previous TLP or RTO. So we need to independently recalculate the RTO time (instead of reading it out of icsk_timeout). Removing this dependency on the nature of icsk_timeout makes things a little easier to reason about anyway. Note that the old and new code should be equivalent, since they are both saying: "if the RTO is in the future, but at an earlier time than the normal TLP time, then set the TLP timer to fire when the RTO would have fired". Fixes: 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)") Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Nandita Dukkipati --- net/ipv4/tcp_output.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 2f1588bf73da..0ae6b5d176c0 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2377,8 +2377,8 @@ bool tcp_schedule_loss_probe(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); - u32 timeout, tlp_time_stamp, rto_time_stamp; u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3); + u32 timeout, rto_delta_us; /* No consecutive loss probes. */ if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) { @@ -2418,13 +2418,9 @@ bool tcp_schedule_loss_probe(struct sock *sk) timeout = max_t(u32, timeout, msecs_to_jiffies(10)); /* If RTO is shorter, just schedule TLP in its place. */ - tlp_time_stamp = tcp_jiffies32 + timeout; - rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout; - if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) { - s32 delta = rto_time_stamp - tcp_jiffies32; - if (delta > 0) - timeout = delta; - } + rto_delta_us = tcp_rto_delta_us(sk); /* How far in future is RTO? */ + if (rto_delta_us > 0) + timeout = min_t(u32, timeout, usecs_to_jiffies(rto_delta_us)); inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout, TCP_RTO_MAX); -- 2.14.0.rc0.400.g1c36432dff-goog