netdev - Re: [PATCH net-next 1/2] tcp: measure rwnd-limited time

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Date:   Wed, 7 Sep 2016 01:07:21 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     "Francis Y. Yan" <francisyyan@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next 1/2] tcp: measure rwnd-limited time

On Tue, Sep 6, 2016 at 9:32 PM, Francis Y. Yan <francisyyan@...il.com> wrote:
> This patch measures the total time when TCP transmission is limited
> by receiver's advertised window (rwnd), and exports it in tcp_info as
> tcpi_rwnd_limited.
>
> The rwnd-limited time is defined as the period when the next segment
> to send by TCP cannot fit into rwnd. To measure it, we record the last
> timestamp when limited by rwnd (rwnd_limited_ts) and the total
> rwnd-limited time (rwnd_limited) in tcp_sock.
>
> Then we export the total rwnd-limited time so far in tcp_info, where
> by so far, we mean that if TCP transmission is still being limited by
> rwnd, the time interval since rwnd_limited_ts needs to be counted as
> well; otherwise, we simply export rwnd_limited.
>
> It is worth noting that we also have to add a new sequence counter
> (seqcnt) in tcp_sock to carefully handle tcp_info's reading of
> rwnd_limited_ts and rwnd_limited in order to get a consistent snapshot
> of both variables together.
>
> Signed-off-by: Francis Y. Yan <francisyyan@...il.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>