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tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy

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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 <jmaxwell37@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jon Maxwell 2018-07-19 11:14:44 +10:00 committed by David S. Miller
parent a7fa37703d
commit b701a99e43
1 changed files with 17 additions and 1 deletions
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18
net/ipv4/tcp_timer.c
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@ -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 @@ out_reset_timer:
/* 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);