From: Stephen Hemminger <shemminger@osdl.org>
To: "Xiaoliang (David) Wei" <davidwei79@gmail.com>
Cc: "Injong Rhee" <rhee@eos.ncsu.edu>,
"David S. Miller" <davem@davemloft.net>,
"Sangtae Ha" <sha2@ncsu.edu>,
netdev@vger.kernel.org
Subject: Re: TCP congestion graphs (2.6.19-rc4)
Date: Tue, 31 Oct 2006 16:10:07 -0800 [thread overview]
Message-ID: <20061031161007.0fdf5c63@freekitty> (raw)
In-Reply-To: <7335583a0610311525h10cf4e75x42e421d3eb6f53aa@mail.gmail.com>
On Tue, 31 Oct 2006 15:25:16 -0800
"Xiaoliang (David) Wei" <davidwei79@gmail.com> wrote:
> On 10/31/06, Stephen Hemminger <shemminger@osdl.org> wrote:
> > I reran the tests, this time using my DSL line to home (80ms 1Mbit/sec).
> > http://developer.osdl.org/shemminger/tcp/2.6.19-rc4/dsl
> >
> > The only obvious problem is Vegas looks broken.
>
> Thanks, Stephen.
>
> It seems that the default Vegas alpha parameter in the rc4 is 1...
>
> I observed similar situation with the NS2Linux simulator (with 2.6.16
> code) and found that if alpha=1, delayed ack will make it broken
> (keeping cwnd very low without real congestion)
>
> See details at http://www.cs.caltech.edu/%7Eweixl/technical/ns2linux/known_linux/index.html#vegas
>
> (Basically alpha==1 means Vegas seeks to see a delay of about 1 packet
> worth. With delayed ack, 1 packet worth of delay is common even with
> no congestion.)
>
> To make Vegas work, I'd suggest to raise alpha to at least 2 or 3.
> (and beta has to be at least as large as alpha.)
>
> -David
>
I ran with the current default:
alpha = 1 (scaled 2)
beta = 3 (scaled 6)
gamma = 1 (scaled 2)
--
Stephen Hemminger <shemminger@osdl.org>
next prev parent reply other threads:[~2006-11-01 0:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-25 18:02 TCP congestion graphs Stephen Hemminger
2006-10-25 22:34 ` Injong Rhee
2006-10-26 1:30 ` Stephen Hemminger
2006-10-26 18:50 ` Hagen Paul Pfeifer
2006-10-26 19:36 ` Stephen Hemminger
2006-10-31 20:00 ` TCP congestion graphs (2.6.19-rc4) Stephen Hemminger
2006-10-31 23:25 ` Xiaoliang (David) Wei
2006-11-01 0:10 ` Stephen Hemminger [this message]
2006-11-01 1:30 ` David Miller
2006-11-01 5:25 ` Evgeniy Polyakov
2006-11-01 5:58 ` Stephen Hemminger
2006-11-02 5:44 ` David Miller
2006-11-02 19:58 ` Stephen Hemminger
2006-11-28 22:38 ` David Miller
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