netdev - Re: [PATCH net-next] tcp: expose both send and receive intervals for rate sample

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Date:   Mon, 9 Jul 2018 09:23:23 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Deepti Raghavan <deeptir@....edu>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: expose both send and receive intervals for
 rate sample

On Mon, Jul 9, 2018 at 9:05 AM, Deepti Raghavan <deeptir@....edu> wrote:
> Congestion control algorithms, which access the rate sample
> through the tcp_cong_control function, only have access to the maximum
> of the send and receive interval, for cases where the acknowledgment
> rate may be inaccurate due to ACK compression or decimation. Algorithms
> may want to use send rates and receive rates as separate signals.
>
> Signed-off-by: Deepti Raghavan <deeptir@....edu>
Acked-by: Yuchung Cheng <ycheng@...gle.com>
> ---
>  include/net/tcp.h   | 2 ++
>  net/ipv4/tcp_rate.c | 4 ++++
>  2 files changed, 6 insertions(+)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index cce3769..f6cb20e 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -954,6 +954,8 @@ struct rate_sample {
>   u32  prior_delivered; /* tp->delivered at "prior_mstamp" */
>   s32  delivered; /* number of packets delivered over interval */
>   long interval_us; /* time for tp->delivered to incr "delivered" */
> + u32 snd_interval_us; /* snd interval for delivered packets */
> + u32 rcv_interval_us; /* rcv interval for delivered packets */
>   long rtt_us; /* RTT of last (S)ACKed packet (or -1) */
>   int  losses; /* number of packets marked lost upon ACK */
>   u32  acked_sacked; /* number of packets newly (S)ACKed upon ACK */
> diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
> index c61240e..4dff40d 100644
> --- a/net/ipv4/tcp_rate.c
> +++ b/net/ipv4/tcp_rate.c
> @@ -146,6 +146,10 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32
> lost,
>       rs->prior_mstamp); /* ack phase */
>   rs->interval_us = max(snd_us, ack_us);
>
> + /* Record both segment send and ack receive intervals */
> + rs->snd_interval_us = snd_us;
> + rs->rcv_interval_us = ack_us;
> +
>   /* Normally we expect interval_us >= min-rtt.
>    * Note that rate may still be over-estimated when a spuriously
>    * retransmistted skb was first (s)acked because "interval_us"
> --
> 2.7.4
>