Date: Fri, 29 Jan 2016 13:51:21 -0800 From: hiren panchasara <hiren@strugglingcoder.info> To: Yongmin Cho <yongmincho82@gmail.com> Cc: transport@freebsd.org Subject: Re: Restarting Idle Connections Message-ID: <20160129215121.GJ33155@strugglingcoder.info> In-Reply-To: <20160129043817.GA9865@yongmincho-All-Series> References: <20160129043817.GA9865@yongmincho-All-Series>
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On 01/29/16 at 01:38P, Yongmin Cho wrote:
> Hi, all.
>=20
> 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.
>=20
> 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 =3D 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)
rw =3D min(4 * CCV(ccv, t_maxseg),
max(2 * CCV(ccv, t_maxseg), 4380));
Any inputs?
Cheers,
Hiren
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