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Date:      Mon, 03 Apr 2006 15:23:12 -0600
From:      Scott Long <scottl@samsco.org>
To:        Steve Kargl <sgk@troutmask.apl.washington.edu>
Cc:        freebsd-amd64@freebsd.org
Subject:   Re: Status of NX bit support.
Message-ID:  <44319240.8070203@samsco.org>
In-Reply-To: <20060403211943.GA99241@troutmask.apl.washington.edu>
References:  <44301C6D.3010206@rogers.com> <200604031442.43477.jhb@freebsd.org>	<44318E3F.6080808@rogers.com> <20060403211943.GA99241@troutmask.apl.washington.edu>

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Steve Kargl wrote:
> On Mon, Apr 03, 2006 at 05:06:07PM -0400, Mike Jakubik wrote:
> 
>>John Baldwin wrote:
>>
>>>On Sunday 02 April 2006 14:48, Mike Jakubik wrote:
>>> 
>>>
>>>>I was wondering what the status of the NX bit support is. Is the pmap.c 
>>>>code still broken or is support enabled and functioning by default?
>>>>   
>>>
>>>I don't think the status has changed.
>>>
>>> 
>>
>>Well that sucks.. I guess then there really is no reason for someone to 
>>run in amd64 mode unless you need more than 4GB of ram.
>>
> 
> 
> You're joking, right?  How many registers are available for the
> i386?  How many registers are available to an AMD64 cpu in 
> 64-bit mode?
> 

You also get less efficient cache utilization due to the wider data
types that are in use.  It seems to be mostly a wash between the
advantages of more registers and the cost of lower cache efficiency.
amd64 is nice when you need more kernel address space and/or more
process address space.

Scott




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