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From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Pyun YongHyeon <pyunyh@gmail.com>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: is RTL8139 THAT bad?
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>>
>> Why it's THAT bad?
>>
>
> Because CPU always have to copy frames to/from the controller.

comment says card do DMA. just then it has to copy but within main memory 
not PCI.

> These CPU cycles could have been used in other task to give more
> performance such as SSH encryption/decryption, checksum computation
> etc.
>
>> 3.5MB/s is less that 2500 packets/second. 50% at 200Mhz means 100000000
>> cycles spend on interrupt service, which is 40000 CPU cycles per packet.
>>
>
> That depends on your application. It would be ok for normal desktop
> PCs with fast CPU but it wouldn't be acceptable on servers that
> have to do lots of other processing. If you have fxp(4) or txp(4)

i know all this, but i'm asking why processing single interrupt takes 
40000 CPU cycles.