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Date: Thu, 03 Jul 2008 14:57:09 +0200
From: Kris Kennaway <kris@FreeBSD.org>
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To: Zbigniew Szalbot <z.szalbot@lc-words.com>
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Cc: User Questions <freebsd-questions@freebsd.org>
Subject: Re: 7.0-release / systat / 3GB
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Zbigniew Szalbot wrote:
> Hello,
> 
> Kris Kennaway:
>> Wojciech Puchar wrote:
>>>> I am a bit curious though why once the outgoing bandwidth exceeds 
>>>> (more or less) 3GB, the Total counter gets reset and starts counting 
>>>> from scratch.
>>> isn't it 4GB - because of 32-bit unsigned counter?
>>
>> I would guess so.
>>
>> Using a 64-bit counter on 32-bit systems would cause additional 
>> processing overhead for little benefit.
> 
> I have confirmed (with assistance from Wojtek Puchar) that the problem 
> of resetting a Total counter for 'systat -ifstat' happens every 4GB (not 
> 3GB) amount of data. It only affects i386 machines. amd64 machines are 
> not affected.
> 
> I have tested this on 7.0 and 6.1-Release versions. Here's an example
> 
> em0  in    104.564 KB/s        104.564 KB/s            2.401 GB
>      out   220.282 KB/s        284.090 KB/s            3.874 GB
> 
> em0  in     17.416 KB/s        220.306 KB/s            2.404 GB
>      out   257.781 KB/s        284.090 KB/s            3.902 GB
> 
> em0  in     35.181 KB/s        803.832 KB/s            2.420 GB
>      out   170.575 KB/s        284.090 KB/s            3.980 GB
> 
> em0  in     11.020 KB/s        803.832 KB/s            2.423 GB
>      out    27.773 KB/s        284.090 KB/s            3.998 GB
> 
> em0  in      5.515 KB/s        803.832 KB/s            2.423 GB
>      out    97.953 KB/s        284.090 KB/s            4.000 GB
> 
> em0  in      7.944 KB/s        803.832 KB/s            2.423 GB
>      out    71.475 KB/s        284.090 KB/s           25.019 KB
> 
> I have submitted a pr in case this can be fixed.
> 
> http://www.freebsd.org/cgi/query-pr.cgi?pr=125196

I explained above why it cannot reasonably be fixed on i386 :-)

Kris