Hi:
TCP only sends a packet if:
tcp_packets_in_flight(tp) < tp->snd_cwnd
(function tcp_snd_test in include/net/tcp.h)
but regards transmission as application-limited if
tp->packets_out < tp->snd_cwnd
(function tcp_cwnd_validate in include/net/tcp.h)
So the kernel _always_ thinks the connection is
application-limited, forcing many un-necessary
reductions in the size of the congestion window.
I think the condition in tcp_snd_test should be:
tcp_packets_in_flight(tp) <= tp->snd_cwnd
Mark
Mark Reginald James writes:
> TCP only sends a packet if:
>
> tcp_packets_in_flight(tp) < tp->snd_cwnd
>
> (function tcp_snd_test in include/net/tcp.h)
>
> but regards transmission as application-limited if
>
> tp->packets_out < tp->snd_cwnd
>
> (function tcp_cwnd_validate in include/net/tcp.h)
>
> So the kernel _always_ thinks the connection is
> application-limited
Why? After the final "send a packet if" test, tp->packets_out will be
incremented and thus be equal to tp->snd_cwnd, marking the connection
as _not_ application limited.
Later,
David S. Miller
[email protected]