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To: "Brian J. McGovern" <mcgovern@spoon.beta.com>
cc: questions@freebsd.org
Subject: Re: Cyclades cards (hardware question) 
In-reply-to: Your message of "Tue, 17 Dec 1996 08:38:53 EST."
             <199612171338.IAA24038@spoon.beta.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Tue, 17 Dec 1996 07:07:21 -0800
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>while FTP'ing files across all 16 ports at the same time. Running TOP,
>the "interrupt" CPU time can approach as high as 24% on a 586/133. The overruns
>seem to sync. up with the drive writes from the FTP sessions.
>
>Now, my thoughts are to switch to PCI cards with less density - 2 16 port PCI
>cards), or possibly 4 8 port cards (PCI) to alleviate the problem. However,
>I don't want to drive the cost up by requiring mode interface cards if its
>not going to help the real problem - which may just be that I shouldn't be
>hitting the hard disk while streaming these cards. At the same time, I'm
>thinking if these cards are doing DMA to offload their data, the PCI Bus
>will help immensely. However, I worry that if I then double my port capacity
>to 32 per PC, I don't want to take what I've gained and lose a lot more.

   The PCI cards use shared memory just like the ISA cards...no DMA. If the
cards are configured to map the memory >1MB, then the shared memory speed may
be as much as 3 times that of the ISA equivilent. Cyclades has been shipping
the PCI cards to map the shared memory in the 640K-1MB region, so if you do
get the PCI card, make sure you change the setting via the "cytest.exe"
program that Cyclades has on their FTP site.

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project