Re: GNAT compiler switches and optimization

[Jeffrey Creem <jeff@thecreems.com>]

Jeffrey R. Carter wrote:
> Jeffrey Creem wrote:
> 
>>
>> 2) Small changes to the original code that still meet the original 
>> structure and intent of the original code can move the run time up and 
>> down by at least 50%
>> 3) The two task based version of the code is running more than 2x 
>> faster than the single task version on a 2 processor machine. Some of 
>> this is from the two tasks but looking at the assembly, another 
>> portion of it is  related to #2 above in that the re-arrangement of 
>> the math allows the compiler to get less brain dead.
> 
> 
> These seem quite odd to me. Perhaps whatever is causing this is also the 
> cause of the speedup I saw in the sequential case when the 
> multiplication is put in a procedure.
> 

Ok, we are all probably tired of taking about this topic but I posted 
what I think will be the final write-up on this (until the bugzilla 
issue for it is resolved).

http://gnuada.sourceforge.net/pmwiki.php/Main/Oct2006CLAGFORTRANComparison

And I agree that the > 2x speedup for the two task version is not real. 
There are now other versions that are coded in a similar maner to the 2 
task version but which are single threaded. The 2 task version runs 
almost exactly 2x faster (sometimes slightly slower) on my dual 
processor machine.