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authorNeal Cardwell <ncardwell@google.com>2017-08-03 09:19:53 -0400
committerDavid S. Miller <davem@davemloft.net>2017-08-03 15:38:30 -0700
commita2815817ffa68c7933a43eb55836d6e789bd4389 (patch)
treef8d6bda5f3b60b508ffc9b9ceac83b5c9a17570b /net
parente1a10ef7fa876f8510aaec36ea5c0cf34baba410 (diff)
downloadlwn-a2815817ffa68c7933a43eb55836d6e789bd4389.tar.gz
lwn-a2815817ffa68c7933a43eb55836d6e789bd4389.zip
tcp: enable xmit timer fix by having TLP use time when RTO should fire
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> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_output.c14
1 files changed, 5 insertions, 9 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 2f1588bf73da..cd8e257492c4 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)) {
@@ -2417,14 +2417,10 @@ bool tcp_schedule_loss_probe(struct sock *sk)
(rtt + (rtt >> 1) + TCP_DELACK_MAX));
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;
- }
+ /* If the RTO formula yields an earlier time, then use that time. */
+ 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);