kern/154428: xn0 network interface and PF - Massive performance drop

[Alex]

On 02/01/11 16:40, Alex wrote:
> The following reply was made to PR kern/154428; it has been noted by GNATS.
>
> From: Alex<joovke at joovke.com>
> To: bug-followup at FreeBSD.org
> Cc:
> Subject: Re: kern/154428: xn0 network interface and PF - Massive performance
>   drop
> Date: Tue, 01 Feb 2011 14:29:58 +1100
>
>   Confirmed problem still evident in 8.2 RC3 (did a full source csup and
>   buildworld).
>
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Fixed by net.inet.tcp.tso: 1 -> 0

but why?? found this by trial an error.  setting net.inet.tcp.tso to 0 
with pf enabled gives good performance, if i set it to 1, speeds plumet 
to below dialup!