[arch-general] ?rch x86_64 and i686 performance comparison

[Sven-Hendrik Haase]

On 11.11.2009 17:53, Andreas Radke wrote:
> Am Wed, 11 Nov 2009 17:44:53 +0100
> schrieb Dieter Plaetinck <dieter at plaetinck.be>:
>
>   
>> On Wed, 11 Nov 2009 17:18:12 +0100
>> Sven-Hendrik Haase <sh at lutzhaase.com> wrote:
>>
>>     
>>> You will probably see the
>>> opposite of what you saw in the VMs. Especially for video encoding,
>>> x86_64 will be noticeably faster.
>>>       
>> why is that?
>>
>>     
>
> should be because of SSE+SSE2 extensions that are included in our
> default compiler flags that are not used in i686.
>
> -Andy
>
>   
I've been searching for info on that but so far I couldn't find
anything. Usually, SSE instructions flags are enabled specifically in
the Makefiles of the programs that actually make use of them. They are
not universally enabled in every compiled program by default (according
to the optimizations turned on by -O2).
Can you elaborate what you mean? Why are they not used on i686?