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

On Tue, Sep 6, 2016 at 9:32 PM, Francis Y. Yan [off-list ref] 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 <redacted>
Signed-off-by: Yuchung Cheng <redacted>

Acked-by: Soheil Hassas Yeganeh <redacted>