Restarting Idle Connections

[hiren panchasara]

On 01/29/16 at 01:51P, hiren panchasara wrote:
> On 01/29/16 at 01:38P, Yongmin Cho wrote:
> > Hi, all.
> > 
> > I have an opinion about net.inet.tcp.initcwnd_segments.
> > You know, snd_cwnd is restarted transmission after a long idle
> > period(Current RTO).
> > And, All of congestion control algorithm is using newreno_after_idle
> > function after a long idle period.
> > But, The newreno_after_idle function is not using initcwnd_segments.
> > I think, The initcwnd_segments should be used in newreno_after_idle
> > function, If the newreno_after_idle is called.
> > I referred to rfc6928.
> > 
> > Please check my opinion.
> 
> You are absolutely right. We (FreeBSD) adopted initcwnd to be 10
> segments but never bothered to update newreno_after_idle() function to
> reflect that in calculating cwnd after idle period. Though the comments
> in that function clearly says:
> "The restart window is the initial window or the last CWND, whichever is
> smaller."
> 
> I think we should make following change to accommodate it:
> 
> diff --git a/sys/netinet/cc/cc_newreno.c b/sys/netinet/cc/cc_newreno.c
> index 97ec35f..5210a45 100644
> --- a/sys/netinet/cc/cc_newreno.c
> +++ b/sys/netinet/cc/cc_newreno.c
> @@ -166,6 +166,10 @@ newreno_after_idle(struct cc_var *ccv)
>          *
>          * See RFC5681 Section 4.1. "Restarting Idle Connections".
>          */
> +       if (V_tcp_initcwnd_segments)
> +               rw = min(V_tcp_initcwnd_segments * CCV(ccv, t_maxseg),
> +                   max(2 * CCV(ccv, t_maxseg),
> +                       V_tcp_initcwnd_segments * 1460));
 -       if (V_tcp_do_rfc3390)
 +       else if (V_tcp_do_rfc3390) 

But you get the idea. :-)

Cheers,
Hiren
>                 rw = min(4 * CCV(ccv, t_maxseg),
>                     max(2 * CCV(ccv, t_maxseg), 4380));
> 
> Any inputs?
> 
> Cheers,
> Hiren

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