[mythtv-users] MythTV Compile Options

[Brian Wood]

On Feb 6, 2006, at 9:24 PM, Steven Adeff wrote:
>
> I've got two systems running Debian64 both using mmx w/ no problems.
>

OK, real empirical info is great.

A bit OT, but a lot of people are running amd64 CPUs with MythTV  
systems, some in 64-bit and some in 32-bit mode (knoppmyth comes to  
mind).

What concerns me is (from en.wikipedia.org):

"...however, if they're used in 32-bit programs, those programs will  
only work on systems with processors that support them. This is not  
an issue in 64-bit programs, as all processors that support AMD64  
support SSE and SSE2, so using SSE and SSE2 instructions instead of  
x87 instructions doesn't reduce the set of machines on which the  
programs will run. Since SSE and SSE2 are generally faster than, and  
duplicate most of the features of, the traditional x87 instructions,  
MMX, and 3DNow!, the latter are redundant under AMD64."

"Most" is not "all" when it comes to instructions.

Also (same source):

"Nevertheless, the most recent documentation available from Microsoft  
states that the x87/MMX/3DNow! instructions may not be used in long  
mode."

Although granted this would likely refer only to Windows, it was  
enough for me to be concerned, especially as it is not uncommon for  
Windows codecs to be used on Linux systems.

So the "problems" that might be encountered would likely only be with  
specific codecs or other apps that were specifically written to use  
mmx, that just happened to use an instruction that was not included  
in "most", and thus might be very rare and hard to pin down.

Just the kind of bug that would be *very* difficult to figure out.

Then there is the question of why Gentoo disables mmx on amd64s.

Anyway, soapbox mode off, I beg the groups forgiveness but I really  
want to know what going on here.