Re: C vs C++

I would suggest you submit this as a bug to IBM.

While some difference in performance is understandable, a 2X difference is not acceptable.

Report it and see what IBM have to say.


Jon Paris

www.partner400.com
www.SystemiDeveloper.com

On Feb 16, 2015, at 11:00 AM, Jevgeni Astanovski <[email protected]> wrote:

> No chance, Charles.
> All three are compiled in 2 phases and all three use ACTGRP(*CALLER).
> 
> 
> On Mon, Feb 16, 2015 at 5:10 PM, Charles Wilt <[email protected]> wrote:
>> Any chance your C++ programs are using ACTGRP(*NEW) and the C ones are not?
>> 
>> Charles
>> 
>> On Mon, Feb 16, 2015 at 9:56 AM, Jevgeni Astanovski <[email protected]>
>> wrote:
>> 
>>> Hi all.
>>> Does anyone have any idea why C++ program is significantly slower than
>>> C program?
>>> 
>>> Explain the situation.
>>> I have a number of API-s that are called via RPC, access some tables,
>>> make some calculations and return some structures to the caller.
>>> They've all been written on ILE/C.
>>> Recently I started to experiment with porting them to ILE/C++. There
>>> was a number of reasons why it would be nice.
>>> After I rewrote the first one, I started to measure performance. This
>>> is an issue for me as some of them are called hundreds of thousands
>>> times per day.
>>> Found out that it is approximately 2 times slower than C version.
>>> Shared a code to colleges - no one found anything suspicious. However
>>> one guy came out with a "brilliant" idea - he advised me to try to
>>> recompile my C program with CPP compiler and see the performance.
>>> Guess what? C program compiled with CPP compiler was the same 2 times
>>> slower than C program compiled with C compiler....
>>> 
>>> And the only modifications that I did for compiling C with CPP compiler
>>> was:
>>> 1. Substituted "#pragma mapinc" table structue definitions with those
>>> generated by GENCSRC;
>>> 2. Changed char and unsigned char in a couple of places as C++ is more
>>> strict;
>>> 3. Made a substitution for "NNNND" constants (like 100D for example)
>>> as C++ does not support that.
>>> 
>>> What I saw is that time increase looks like it has a proportional nature.
>>> I tested API in 3 cases (number of tests is over 100): simple request,
>>> medium request; complicated request and the timing is:
>>> Simple C: 1ms; Simple C++ : 2ms
>>> Medium C: 3ms; Simple C++ : 7ms
>>> Long C: 25ms; Long C++: 60ms.
>>> 
>>> The difference is in number of records read from table and a number of
>>> calculations.
>>> That is a simple one retrieves less that 10 records; medium - more
>>> than 10 and long - more than 100. Program makes a lot of calculations
>>> with packed decimal.
>>> 
>>> Any idea why it is like that and is there anything that can be done about
>>> it?
>>> 
>>> Thanks in advance,
>>> 
>>> Jevgeni.
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