[LAD] optimum binary distribution

[James Courtier-Dutton]

Christian Schoenebeck wrote:
> Am Mittwoch, 16. April 2008 22:41:36 schrieben Sie:
>> You are not really following what I am trying to get across.  Cross
>> compilation isn't the issue.  The issue is that something as generic as
>> i386 (or i686 for rpm based distros IIRC) actually targets a lot of
>> different types of hardware. It can run on pretty old pentium based CPUs,
>> but also modern
>> systems.  A binary distributor has no way of knowing which
>> CPU is going to be used, in fact, a single binary package
>> is going to be used by many of the supported variants.
> 
> Trust me, I can follow what you mean and I also thought about a solution for 
> that problem years ago. The point is, where do you draw the line? You might 
> say, for the x86 architecture you detect at runtime whether the system 
> supports: MMX, SSE(1), SSE2, SSE3 and precompile 5 binaries which is going to 
> be picked automatically at application startup. Unfortunately that's not 
> sufficient to achieve max. performance. On some weak systems for example you 
> achieve better results with -Os than with -O3. So wanna make extra binarie(s) 
> and runtime benchmark for that as well? You could continue that game for a 
> lot of other GCC flags and your binary collection would grow to a horrible 
> huge cross product. And we're still just talking about one architecture.
> 
> That's why I was thinking about a little different approach for binary 
> distributions: just precompile some part of the audio application (/most of 
> it) and actually compile the core elements (the ones that are crucial to 
> overall performance) on demand by the user. Because I agree compiling a whole 
> complex audio app is usually an unconvenient user-unfriendly task, especially 
> because all of those library dependencies and system specific path locations 

For audio apps, the only bits that need real optimization are the parts 
that sit in the audio path. I.e. The DSP bits.
These are normally best done with hand crafted code. So, one just 
includes all the different CPU types, e.g. MMX, SSE etc. in one source 
code. Compile it all as one, and then use runtime detection to select 
the correct routine to execute.
For example, this is how most of libffmpeg works.

James