Status of NX bit support.

[Scott Long]

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