From: Neal Cardwell <ncardwell@google•com>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org, Neal Cardwell <ncardwell@google•com>,
Yuchung Cheng <ycheng@google•com>,
Nandita Dukkipati <nanditad@google•com>
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 [thread overview]
Message-ID: <20170801025814.31206-3-ncardwell@google.com> (raw)
In-Reply-To: <20170801025814.31206-1-ncardwell@google.com>
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 <ncardwell@google•com>
Signed-off-by: Yuchung Cheng <ycheng@google•com>
Signed-off-by: Nandita Dukkipati <nanditad@google•com>
---
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
next prev parent reply other threads:[~2017-08-01 2:58 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-01 2:58 [PATCH net 0/3] tcp: fix xmit timer rearming to avoid stalls Neal Cardwell
2017-08-01 2:58 ` [PATCH net 1/3] tcp: introduce tcp_rto_delta_us() helper for xmit timer fix Neal Cardwell
2017-08-01 7:16 ` Eric Dumazet
2017-08-01 2:58 ` Neal Cardwell [this message]
2017-08-01 7:22 ` [PATCH net 2/3] tcp: enable xmit timer fix by having TLP use time when RTO should fire Eric Dumazet
2017-08-01 14:35 ` Neal Cardwell
2017-08-01 20:40 ` Eric Dumazet
2017-08-01 2:58 ` [PATCH net 3/3] tcp: fix xmit timer to only be reset if data ACKed/SACKed Neal Cardwell
2017-08-01 7:25 ` Eric Dumazet
2017-08-01 12:20 ` maowenan
2017-08-01 14:24 ` Neal Cardwell
2017-08-04 7:12 ` maowenan
2017-08-04 15:54 ` Neal Cardwell
2017-08-04 7:33 ` maowenan
2017-08-04 16:59 ` Neal Cardwell
2017-08-04 17:10 ` Willy Tarreau
2017-08-04 18:01 ` Neal Cardwell
2017-08-04 18:18 ` Willy Tarreau
2017-08-06 7:39 ` maowenan
2017-08-06 7:44 ` Willy Tarreau
2017-08-06 15:21 ` Neal Cardwell
2017-08-06 15:24 ` Neal Cardwell
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