difference between MD and MT

difference between MD and MT

Hi everyone,

      i have this code, the i complied it with MT and MD in the Fortran runtime library option. What i obtain is

10 runs with MD: 5.29 seconds in average

10 runs  with MT: 6.5 seconds in average

Anyone has an idea about this difference ? I think the results are supposed to be the same in this case, right?


program perform

implicit none

real x,y

real*8 t1,t2

integer i

call cpu_time(t1)

do i=1,1000000000







call cpu_time(t2)

print *,t2-t1

end program perform



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It's possible that not all time spent in the dynamic library is captured by cpu_time().

Your example doesn't make your motivation clear.  System_clock() would give an indication of actual time spent.

i tried system_clock() to run the code

with MT it takes about 8 senconds and with MD it takes 6 senconds. You have other idea?

thanks a lot

As a benchmark, your code may not do what you intended. At a sufficiently high level of optimization, your DO loop can be completely removed since the variables altered in the loop are not used elsewhere; the values assigned to x and y are also the same for every value of the loop index i.

>>...It's possible that not all time spent in the dynamic library is captured by cpu_time()...

Actually it is a very interesting function because the returned value needs to be divided by a number of threads used during processing ( especially when parallel processing is enabled ). I did a test recently and if 8 threads were used then a total time of processing is cpu_time() / 8. I use dclock() instead to measure time intervals.

/MT compiler option forces compiler to use static libraries with ( possibly ) less processing overheads instead of dynamic libraries which are mapped to the address space of your application.

i think this is happening only for trigonometry  functions

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