FreeLists / openbeos / [openbeos] Re: app_server: MMX/SSE help wanted

[Adi Oanca <adioanca@xxxxxxxxxxxxxx>]

Hi,

Christian Packmann wrote:
> > Now, I have another question(s):
> >    If GCC 3, app_server, media_kit and translators will all use MMX, how 
> >    can we be sure they won't collide with each other?
> >    MMX runs in parallel with the CPU, but which thread has access to MMX 
> >    registers? The kernel also 
> > manages this? How can MMX be used, do we need a separate thread with MMX 
> > loops only?
>
> MMX uses the FP registers to store data; these are saved when a task switch 
> occurs. That was the reason to implement MMX this way, so that it would 
> work with old operating systems without change.
>
> With SSE and its extra registers, you need special OS support so that the 
> registers are correctly stored and recalled during task switches. As long 
> as the kernel supports this, no problem.
> And if SSE works SSE2 should also work, as it doesn't add new registers, 
> but only new commands to work on the 128-bit regs.

    Aha. OK.
        Axel, will our kernel support SSE too? What about HyperThreading(or 
this is == dual processor)?

> >    What about the case where app_server_MMX is compiled with GCC3_MMX ? 
> >    Should GCC MMX support be disabled in this case?
>
> Hm? MMX is nothing special, just some new x86 instructions. As long as the 
> compiler/assembler supports translating them, there shouldn't be any 
> special problems.

	OK, then let me ask you something:
- MMX works in parallel with the CPU?
- that means you can have an algorithm running on the CPU and some loops running on MMX unit at the 
same time?
- If this is the case, there must be a synchronization mechanism.
This is how I thought MMX is used.

BUT, it seems it is used more like this:
- Enter MMX mode.
- Execute MMX_code_loops (CPU is idle this time. (???)).
- Exit MMX mode.
- Continue execution of my thread.
Is this correct?

I made the wrong assumption that MMX is a... core of its own, and that in the same time the CPU 
could process something else. Guess I was wrong!(?)



Adi.