Poor execution speeds using -mno-cygwin g77 option

[Douglas A. Vechinski]

I am experiencing significantly longer exection speeds when compiling 
with g77 under cygwin using the -mno-cygwin option.

I primarily work and develop under Linux.  However, I need to provide a 
user with an executable (of a Fortran program) that runs under windows.  
I initially performed some timing comparisions of the code for a simple 
problem under Linux and then under Cygwin with the code compiled with 
-mno-cygwin.  The same machine was used for all timing comparisions 
(i.e., it was a dual boot machine).  Case A is under Linux (RH 7.3, g77 
2.96).  Case B is under Win2k (Cygwin 1.5.7, g77 3.3.1 using 
-mno-cygwin).  Case C is the same as Case B execept without using the 
-mno-cygwin flag.  Case D is under Win2k and compiled with Digital 
Fortran.  Several executions were performed to get representative 
times.  Furthermore, these times represent a section of the code where 
nothing but calculations are being performed, the code do not do any I/O 
within the section that was timed.

Case A: 28.9 sec   (Linux)
Case B: 95.0 sec   (Cygwin g77 -mno-cygwin)
Case C: 41.0 sec   (Cygwin g77)
Case D: 31.1 sec   (Digital Fortan)

Both Cases B and C were repeated from running within the Cygwin 
environment and from just a standard command prompt shell (so Cygwin was 
not involved except the the cygwin1.dll in the case of C) Even though 
Case C, when the -mno-cygwin flag is not used, the difference is still 
significant. compared to Case A.  I would like to get execution 
performance comparable to Cases A and D from the code when compiled 
using Cygwin.  And Case D is not a route that I can use at this time for 
several reasons.  Does anyone know why there is such a performance 
difference with Cygwin and with the -mno-cygwin option. Is this a Cygwin 
problem, or g77 problem or something else.  I don't recall experiencing 
such differences several years ago  when doing the same thing.

Several thousand executions of this code  are going to  performed, so on 
larger problems the speed difference will become an issue.


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