2018-07-19 01:16:41

by Jon Maxwell

Subject: [PATCH V4 net-next 3/3] tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy

Create the tcp_clamp_rto_to_user_timeout() helper routine. To calculate
the correct rto, so that the TCP_USER_TIMEOUT socket option is more
accurate. Taking suggestions and feedback into account from
Eric Dumazet, Neal Cardwell and David Laight. Due to the 1st commit we
can avoid the msecs_to_jiffies() and jiffies_to_msecs() dance.

Signed-off-by: Jon Maxwell <[email protected]>
---
net/ipv4/tcp_timer.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index d212f183dd2d..a242f8874629 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -36,6 +36,21 @@ u32 tcp_retransmit_stamp(const struct sock *sk)
return start_ts;
}

+static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ u32 elapsed, start_ts;
+
+ start_ts = tcp_retransmit_stamp(sk);
+ if (!icsk->icsk_user_timeout || !start_ts)
+ return icsk->icsk_rto;
+ elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;
+ if (elapsed >= icsk->icsk_user_timeout)
+ return 1; /* user timeout has passed; fire ASAP */
+ else
+ return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(icsk->icsk_user_timeout - elapsed));
+}
+
/**
* tcp_write_err() - close socket and save error info
* @sk: The socket the error has appeared on.
@@ -544,7 +559,8 @@ void tcp_retransmit_timer(struct sock *sk)
/* Use normal (exponential) backoff */
icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
}
- inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ tcp_clamp_rto_to_user_timeout(sk), TCP_RTO_MAX);
if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0))
__sk_dst_reset(sk);

--
2.13.6

2018-07-19 14:17:03

by Eric Dumazet

Subject: Re: [PATCH V4 net-next 3/3] tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy

On 07/18/2018 06:14 PM, Jon Maxwell wrote:
> Create the tcp_clamp_rto_to_user_timeout() helper routine. To calculate
> the correct rto, so that the TCP_USER_TIMEOUT socket option is more
> accurate. Taking suggestions and feedback into account from
> Eric Dumazet, Neal Cardwell and David Laight. Due to the 1st commit we
> can avoid the msecs_to_jiffies() and jiffies_to_msecs() dance.
>
> Signed-off-by: Jon Maxwell <[email protected]>


Signed-off-by: Eric Dumazet <[email protected]>

Thanks !