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Date:      Wed, 17 Jul 1996 14:00:18 -0400
From:      dennis@etinc.com (Dennis)
To:        "Michael L. VanLoon -- HeadCandy.com" <michaelv@HeadCandy.com>
Cc:        hackers@freebsd.org
Subject:   Re: mitsumi CD-ROM 
Message-ID:  <199607171800.OAA24031@etinc.com>

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>>To no-doubt spurn another wide-eyed debate among the academics, I also
>>dont want a bus-mastering controller stealing the bus from my more-critical
>>communications in a router-system where disk functions are secondary.
>
>This makes no sense.  The only time a bus-mastering controller
>"steals" the bus is when you're doing I/O.  An IDE drive not only
>steals the bus by implication, but it steals the CPU as well!
>Basically, IDE steals the entire machine until the I/O is finished.
>At least with a bus-mastering controller, the CPU can run out of the
>cache while a disk transfer is in progress.
>
>I can understand your opinion on this, as stated above.  But to think
>that you're not getting the bus, and the CPU, stolen, when
>bus-mastering would steal only the bus, is a complete
>misunderstanding.

stealing the bus is stealing the cpu when a router is doing largely transfers
from cards. Your cant process packets until you get them. And if the cpu is
in a transfer cycle and cant get the bus then its idle.

I dont want my packet transfers being interrupted by trivial disk activity. An 
IDE will only use the CPU when  it has it already anyway.....a bus-master 
makes the system much less predictable and assumes the wrong priorities.

db
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