[MOAB-dev] Discussion on return type of MOAB routines

[Tim Tautges (ANL)]

Ok, I tried explicit constructor/operator=, and they didn't change things much.  But, I get really different timing for 
the struct or class based version.  I also added a char* member to the class to check that too, without that much 
additional time being required after adding that.  I also changed the #loop iterations to 10^6 and the depth of 
recursion to 10, I think that's more realistic for MOAB.

The times vary somewhat, but representative times are:

class-based version, w/o funcs: .018-.025s (10 runs)
class-based version, with funcs: .017-.030s (10 runs)
POD version: .002-.003s (10 runs)

Code is attached.  Vijay, could you run this too?

Danqing, are you using an NFS-connected disk, or a local one?

- tim

On 01/24/2014 11:50 AM, Wu, Danqing wrote:
> Even with C style struct, without explicitly defined constructors, there is still noticeable difference.
>
> Used g++ -O3 to build.
> For returning plain enum type, the result on my laptop is
> real	0m0.003s
> user	0m0.000s
> sys	0m0.000s
>
> For returning struct, the result is
> real	0m4.114s
> user	0m4.112s
> sys	0m0.000s
>
> //////////////////////////////////////////////
> #include <iostream>
>
> using namespace std;
>
> enum ErrorCode { MB_SUCCESS = 0, MB_FAILURE = 1 };
>
> struct ErrorInfo {
>    ErrorCode mErrorCode;
> };
>
> ErrorCode test_return_0(long n)
> {
>    if (n > 0)
>      return test_return_0(n - 1);
>
>    return MB_SUCCESS;
> }
>
> ErrorInfo test_return_1(long n)
> {
>    if (n > 0)
>      return test_return_1(n - 1);
>
>    return ErrorInfo();
> }
>
> int main()
> {
>    for (long i = 0; i < 100000; i++)
>      test_return_0(100000); // Change to test_return_1(100000) for comparison
>
>    return 0;
> }
> ________________________________________
> From: Jed Brown [jed at jedbrown.org]
> Sent: Friday, January 24, 2014 11:30 AM
> To: Tautges, Timothy J.; Vijay S. Mahadevan
> Cc: Wu, Danqing; Paul Wilson; moab-dev at mcs.anl.gov
> Subject: Re: [MOAB-dev] Discussion on return type of MOAB routines
>
> "Tim Tautges (ANL)" <tautges at mcs.anl.gov> writes:
>
>> Yeah, but even the ErrorCode-only class version was way slower than
>> the one returning only ErrorCode, that's what makes me think there's
>> C++ stuff going on behind the scenes (or optimizations the class
>> version doesn't get) that is causing the big jump.
>
> Where is the exact code?  Also, it should be obvious in the assembly.
>

-- 
================================================================
"You will keep in perfect peace him whose mind is
   steadfast, because he trusts in you."               Isaiah 26:3

              Tim Tautges            Argonne National Laboratory
          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
  phone (gvoice): (608) 354-1459      1500 Engineering Dr.
             fax: (608) 263-4499      Madison, WI 53706

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