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Subject: Re: [net-next, 3/3] tcp: convert icsk_user_timeout from jiffies to
 msecs
To:     Jon Maxwell <jmaxwell37@gmail.com>, davem@davemloft.net
Cc:     edumazet@google.com, ncardwell@google.com, David.Laight@aculab.com,
        kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        jmaxwell@redhat.com
References: <20180713004919.18608-1-jmaxwell37@gmail.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <9a96cc7d-e7bd-5be2-9ce4-e74918773560@gmail.com>
Date:   Mon, 16 Jul 2018 09:00:09 -0700
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On 07/12/2018 05:49 PM, Jon Maxwell wrote:
> The final patch in this series. 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>
> ---
>  net/ipv4/tcp_timer.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index 8ab8c9645294..d4d4b30a6bec 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -36,6 +36,22 @@ 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));

	if (elapsed >= icsk->icsk_user_timeout)
		return 1; /* user timeout has passed; fire ASAP */

	return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(icsk->icsk_user_timeout - elapsed));

Thanks !