Re: Toy computational "benchmark" in Ada (new blog post)

[David Trudgett <dktrudgett@gmail.com>]

Il giorno venerdì 7 giugno 2019 11:42:07 UTC+10, john...@googlemail.com ha scritto:
> 
> On my machine I get a nice improvement over -O3 when I
> take the arrays off the heap, and then use the following 2 flags:
> 
>    -march=native -funroll-loops

That's interesting. Thank you. I'll try that (and your mods below) over the weekend and see what the result is for me.

I thought the -O3 would unroll loops where appropriate. Is that not the case?

I assume that native arch means it will generate optimal instructions for the particular architecture on which the compile is running?

> 
> Modifying the programs is easy:
> 
>  --Values_Array : Values_Array_Access := new Values_Array_Type;
>    Values_Array : Values_Array_Type;
> 
> In the parallel version, change the loop in the task body:
> 
> --       declare
> --          Val : Float64 renames Values_Array (Idx);
> --       begin
>             My_Sum := My_Sum + Values_Array (Idx) ** 2;
> --       end;
> 
> The  -funroll-loops  gave me a nice improvement on the parallel
> program, less so on the serial version. (Makes no sense to me
> at all!) If you are running in a Unix shell, you usually need
> to tell the system if you're going to put giant arrays on the
> stack. I type this on the command line: ulimit -s unlimited.

Ah yes. I used the heap because I didn't want to use such a huge stack (and got the expected error message when I tried anyway). But I wonder why the heap should be any slower? I can't see any reason why it would be.


Regards,
David