Re: Architecture Nomenclature

[Goswin von Brederlow <goswin-v-b@web.de>]

Reinhard Tartler <siretart@debian.org> writes:

> 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
>    pointers
>
>  - "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.

And if nothing else works then compile your source twice, once with SSE2
and once without. You can then use alternatives to let the admin choose
one or the other depending on their hardware.

MfG
        Goswin