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Date:      Thu, 30 Jan 2003 17:46:28 -0700
From:      Scott Long <scott_long@btc.adaptec.com>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        Julian Elischer <julian@elischer.org>, David Schultz <dschultz@uclink.berkeley.edu>, "Andrew R. Reiter" <arr@watson.org>, arch@freebsd.org
Subject:   Re: PAE (was Re: bus_dmamem_alloc_size())
Message-ID:  <3E39C764.3070500@btc.adaptec.com>
In-Reply-To: <Pine.BSF.4.21.0301301059310.35796-100000@InterJet.elischer.org>
References:  <Pine.BSF.4.21.0301301059310.35796-100000@InterJet.elischer.org> <3E39B52E.E46AF9EA@mindspring.com>

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Terry Lambert wrote:

> Julian Elischer wrote:
>
> >The reason for PAE is simple.
> >
> >Disk caches need not be in mapped memory. Physical memory will do.
> >If you want to cache more than  4GB, then PAE is an effective answer.
> >
> >(Assuming I have my TLAs the right way around..)
>
>
> Using the memory by declaring a small copy window that's accessed
> via PAE in the kernel, and not really supporting PAE at all, can
> make this work...

[...]

>
> -- Terry


This troll is totally unneccessary.  Making peripheral devices work with 
PAE is a matter handled between the device driver and the busdma system. 
  Drivers that cannot pass 64 bit bus addresses to their hardware will 
have the data bounced by busdma, just like what happens in the ISA 
world.  The whole point of the busdma push that Robert and Maxime 
started a few months ago is to prepare drivers for the possible coming 
of PAE.
Honestly, though, if you're going to spend the money on a PAE-capable 
motherboard and all the memory to go along with it, are you really going 
to put a Realtek nic and an Advansys scsi card into it?
Also, the PAE work that might happen is not going to affect the vast 
majority of FreeBSD/i386 users at all; I can only imagine that it will 
be a config(8) option that will most likely default to 'off'.
There is nothing to bikeshed here.  Please respect that there are people 
who need PAE, understand PAE, and will happily accept PAE.  Those who do 
not need, understand, or accept it can go along with their lives 
blissfully happy with it turned off.

Scott


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