Re: BicTCP Implementation Bug

[Gene Heskett]

On Monday 21 February 2005 08:47, Yee-Ting Li wrote:
>Hi,
>
>We have discovered a serious implementation bug in BicTCP on the
> Linux kernels. Note that because BicTCP is ON by default, this
> affects all users of kernel versions 2.6.8 and above.
>
>For further details please see:
>http://www.hamilton.ie/net/bic-fix/Linux%20BicTCP.pdf
>
>and the patch is:
>
>Index: linux-2.6.10/include/net/tcp.h
>===================================================================
>--- linux-2.6.10.orig/include/net/tcp.h Fri Dec 24 21:34:00 2004
>+++ linux-2.6.10/include/net/tcp.h      Thu Feb 17 14:13:14 2005
>@@ -1280,8 +1280,7 @@
>                 if (sysctl_tcp_bic_fast_convergence &&
>                     tp->snd_cwnd < tp->bictcp.last_max_cwnd)
>                         tp->bictcp.last_max_cwnd
>-                               = (tp->snd_cwnd *
>(2*BICTCP_1_OVER_BETA-1))
>-                               / (BICTCP_1_OVER_BETA/2);
>+                           = tp->snd_cwnd - ( tp->snd_cwnd /
>(BICTCP_1_OVER_BETA*2) );
>                 else
>                         tp->bictcp.last_max_cwnd = tp->snd_cwnd;

Could this explain why there was a lot of complaining that tcp was 
slower back about then? (2.6.6 release time)

I've built and rebooted to a kernel patched as above, and will report, 
but on my home network, the closest it will come to being congested 
would be during an rsync or amdump from a client run, so it is 
possible I will see no 'get my attention' differences.  Nothing else 
can approach me any faster than a 10base-T circuit.

In case no one else mentions it Mr. Li, patches such as this need a 
"signed off by $yourname" line for record keeping, this just started 
a few months ago.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
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by Gene Heskett are:
Copyright 2005 by Maurice Eugene Heskett, all rights reserved.
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