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Re: Architecture Nomenclature

On Mi, Apr 28, 2010 at 02:07:56 (CEST), Kip Warner wrote:

> On Wed, 2010-04-28 at 00:32 +0200, Benjamin Drung wrote:
>> The best solution would be autodetection of SSE2 on runtime. That can
>> be
>> done with a few lines of code. 
> You're right, that can indeed be done with a few lines of code. e.g.
> cpuid instruction.

SSE2 can be disabled for userland in the kernel. The implementation of
[1] requires this for example.

[1] http://portal.acm.org/citation.cfm?id=1752046.1752053

more safe approach include:

 - "avcodec": installing a SIGILL handler to divert some function

 - "vlc": spawning a child process that does some sse instructions and
   check if it dies.

> The problem is that you then have to perform a branch every time you
> could potentially use hardware acceleration: a condition for when,
> say, SSE2 is available, and another for a generic implementation.
> It isn't ideal performance wise.

If you have both an SSE2 and C only implementation, you can use function
pointers that are set once, not every time the function is called. If
properly implemented, this hardly impacts performance.

> Perhaps for 32-bit x86 architectures where SIMD is required, I could
> build the package for i686 and have it detect at runtime before said is
> actually used, whether it is available or not. If it is not, raise a
> user visible error and terminate.

This can be implemented as SIGILL handler.

> This method assumes the user knows that it is only supported on P4 or
> later generation of x86.

Reinhard Tartler, KeyID 945348A4

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