Parallel jobs using a CMake generated makefile (no speed improvement)

Question

I have been doing some testing on a project that I recently started building with CMake. Before moving to CMake I noticed significant improvements in build time when using the -j option for make with my handwritten Makefile.

Now with CMake I do the same thing and there isn't any noticeable increase in speed. Whether I run with -j or not, I get four processes for make.exe, though only one of them is clocking CPU time and never uses more the 25% of the CPU.

In general, The CMake generated Makefile is much slower than my handwritten Makefile. A quick test shows build times for both CMake and handwritten makefiles with and without the -j flag:

CMake: "make -j all" = 7min
CMake: "make all" = 7min
Handwritten: "make -j all" = 2min
Handwritten: "make all" = 4min

In general, CMake is much slower and doesn't seem to utilize parallel jobs.

Can anyone explain why I'm not seeing any improvements?

(Building a Fortran program with gfortran and using CMake's auto-detect dependency feature...though I don't know if that's relevant to what I'm seeing).

Here's my CMakeLists.txt file:

## CMake Version
cmake_minimum_required(VERSION 2.8)

## Project Name
project(PROJECT)

## Use FORTRAN
enable_language(Fortran)

## Release compiler options
set (CMAKE_Fortran_FLAGS_RELEASE "-O3 -cpp -ffree-line-length-none -fimplicit-none")

## Debug compiler options
set (CMAKE_Fortran_FLAGS_DEBUG "-g -cpp -ffree-line-length-none -fimplicit-none")

## Set directory for FORTRAN modules
set (CMAKE_Fortran_MODULE_DIRECTORY "${PROJECT_BINARY_DIR}/modules")

## Build Executable
add_executable(EXE 
           Source1.f90 
           Source2.f90         
           .
           .
           . 
           Source219.f90
           Source220.f90)

And here's my original Makefile:

PROG = PROGRAM.exe

SRCS = Source1.f90 Source2.f90 ... Source219.o Source220.o

OBJS = Source1.o Source2.o ... Source219.o Source220.o

LIBS =  

VPATH = src
BUILDDIR = debug
F90 = gfortran
F90FLAGS = -g -cpp -ffree-line-length-none -fimplicit-none

all: $(PROG)

$(PROG): $(OBJS)
    $(F90) -o $@ $(OBJS) $(LIBS)


clean:
    erase -f $(BUILDDIR)$(PROG) $(BUILDDIR)\$(OBJS) $(BUILDDIR)\*.mod

.SUFFIXES: $(SUFFIXES) .f90

.f90.o:
     $(F90) $(F90FLAGS) -c $<

Source1.o: Dependency1.o Dependency2.o ... DependencyN.o

Source2.o: Dependency1.o Dependency2.o ... DependencyN.o

.
.
.

Source219.o: Dependency1.o Dependency2.o ... DependencyN.o

Source220.o: Dependency1.o Dependency2.o ... DependencyN.o

Answer 1

Is this on windows? If so it is because the windows version of gmake does not have a job server and recursive makefiles are not parallel. I am assuming that when you wrote make.exe that means windows. I think CVS gmake has a jobs server now. The cygwin gmake also supports the job server.

This link might help you:

http://lists.gnu.org/archive/html/make-w32/2011-07/msg00002.html