Compiling with g using multiple cores

Question

Quick question  what is the compiler flag to allow g   to spawn multiple instances of itself in order to compile large projects quicker  for example 4 source files at a time for a multi-core CPU

User · Answer

People have mentioned make but bjam also supports a similar concept   Using bjam -jx instructs bjam to build up to x concurrent commands   We use the same build scripts on Windows and Linux and using this option halves our build times on both platforms   Nice

User · Answer

I m not sure about g    but if you re using GNU Make then  make -j N   where N is the number of threads make can create  will allow make to run multple g   jobs at the same time  so long as the files do not depend on each other

User · Answer

I m not sure about g    but if you re using GNU Make then  make -j N   where N is the number of threads make can create  will allow make to run multple g   jobs at the same time  so long as the files do not depend on each other

User · Answer

People have mentioned make but bjam also supports a similar concept   Using bjam -jx instructs bjam to build up to x concurrent commands   We use the same build scripts on Windows and Linux and using this option halves our build times on both platforms   Nice

User · Answer

distcc can also be used to distribute compiles not only on the current machine  but also on other machines in a farm that have distcc installed

User · Answer

There is no such flag  and having one runs against the Unix philosophy of having each tool perform just one function and perform it well  Spawning compiler processes is conceptually the job of the build system  What you are probably looking for is the -j  jobs  flag to GNU make  a la  make -j4  Or you can use pmake or similar parallel make systems

User · Answer

You can do this with make - with gnu make it is the -j flag  this will also help on a uniprocessor machine    For example if you want 4 parallel jobs from make   make -j 4   You can also run gcc in a pipe with   gcc -pipe   This will pipeline the compile stages  which will also help keep the cores busy   If you have additional machines available too  you might check out distcc  which will farm compiles out to those as well

User · Answer

You can do this with make - with gnu make it is the -j flag  this will also help on a uniprocessor machine    For example if you want 4 parallel jobs from make   make -j 4   You can also run gcc in a pipe with   gcc -pipe   This will pipeline the compile stages  which will also help keep the cores busy   If you have additional machines available too  you might check out distcc  which will farm compiles out to those as well

User · Answer

You can do this with make - with gnu make it is the -j flag  this will also help on a uniprocessor machine    For example if you want 4 parallel jobs from make   make -j 4   You can also run gcc in a pipe with   gcc -pipe   This will pipeline the compile stages  which will also help keep the cores busy   If you have additional machines available too  you might check out distcc  which will farm compiles out to those as well

User · Answer

If using make  issue with -j  From man make      -j  jobs   --jobs  jobs         Specifies the number of jobs  commands  to run simultaneously           If there is more than one -j option  the last one is effective         If the -j option is given without an argument  make will not limit the        number of jobs that can run simultaneously     And most notably  if you want to script or identify the number of cores you have available  depending on your environment  and if you run in many environments  this can change a lot  you may use ubiquitous Python function cpu count     https   docs python org 3 library multiprocessing html multiprocessing cpu count  Like this   make -j   python3 -c  import multiprocessing as mp  print int mp cpu count     1 5       If you re asking why 1 5 I ll quote user artless-noise in a comment above      The 1 5 number is because of the noted I O bound problem  It is a rule of thumb  About 1 3 of the jobs will be waiting for I O  so the remaining jobs will be using the available cores  A number greater than the cores is better and you could even go as high as 2x

User · Answer

I m not sure about g    but if you re using GNU Make then  make -j N   where N is the number of threads make can create  will allow make to run multple g   jobs at the same time  so long as the files do not depend on each other

User · Answer

I m not sure about g    but if you re using GNU Make then  make -j N   where N is the number of threads make can create  will allow make to run multple g   jobs at the same time  so long as the files do not depend on each other

User · Answer

GNU parallel  I was making a synthetic compilation benchmark and couldn t be bothered to write a Makefile  so I used   sudo apt-get install parallel ls   grep -E    c     parallel -t --will-cite  gcc -c -o      o          Explanation        takes the input argument and removes its extension -t prints out the commands being run to give us an idea of progress --will-cite removes the request to cite the software if you publish results using it      parallel is so convenient that I could even do a timestamp check myself   ls   grep -E    c     parallel -t --will-cite      if     -f      o              -nt      o     then     gcc -c -o      o         fi     xargs -P can also run jobs in parallel  but it is a bit less convenient to do the extension manipulation or run multiple commands with it  Calling multiple commands through xargs  Parallel linking was asked at  Can gcc use multiple cores when linking   TODO  I think I read somewhere that compilation can be reduced to matrix multiplication  so maybe it is also possible to speed up single file compilation for large files  But I can t find a reference now   Tested in Ubuntu 18 10

User · Answer

There is no such flag  and having one runs against the Unix philosophy of having each tool perform just one function and perform it well  Spawning compiler processes is conceptually the job of the build system  What you are probably looking for is the -j  jobs  flag to GNU make  a la  make -j4  Or you can use pmake or similar parallel make systems

User · Answer

If using make  issue with -j  From man make      -j  jobs   --jobs  jobs         Specifies the number of jobs  commands  to run simultaneously           If there is more than one -j option  the last one is effective         If the -j option is given without an argument  make will not limit the        number of jobs that can run simultaneously     And most notably  if you want to script or identify the number of cores you have available  depending on your environment  and if you run in many environments  this can change a lot  you may use ubiquitous Python function cpu count     https   docs python org 3 library multiprocessing html multiprocessing cpu count  Like this   make -j   python3 -c  import multiprocessing as mp  print int mp cpu count     1 5       If you re asking why 1 5 I ll quote user artless-noise in a comment above      The 1 5 number is because of the noted I O bound problem  It is a rule of thumb  About 1 3 of the jobs will be waiting for I O  so the remaining jobs will be using the available cores  A number greater than the cores is better and you could even go as high as 2x

User · Answer

People have mentioned make but bjam also supports a similar concept   Using bjam -jx instructs bjam to build up to x concurrent commands   We use the same build scripts on Windows and Linux and using this option halves our build times on both platforms   Nice

User · Answer

make will do this for you   Investigate the -j and -l switches in the man page   I don t think g   is parallelizable

User · Answer

There is no such flag  and having one runs against the Unix philosophy of having each tool perform just one function and perform it well  Spawning compiler processes is conceptually the job of the build system  What you are probably looking for is the -j  jobs  flag to GNU make  a la  make -j4  Or you can use pmake or similar parallel make systems

User · Answer

distcc can also be used to distribute compiles not only on the current machine  but also on other machines in a farm that have distcc installed

User · Answer

make will do this for you   Investigate the -j and -l switches in the man page   I don t think g   is parallelizable

User · Answer

GNU parallel  I was making a synthetic compilation benchmark and couldn t be bothered to write a Makefile  so I used   sudo apt-get install parallel ls   grep -E    c     parallel -t --will-cite  gcc -c -o      o          Explanation        takes the input argument and removes its extension -t prints out the commands being run to give us an idea of progress --will-cite removes the request to cite the software if you publish results using it      parallel is so convenient that I could even do a timestamp check myself   ls   grep -E    c     parallel -t --will-cite      if     -f      o              -nt      o     then     gcc -c -o      o         fi     xargs -P can also run jobs in parallel  but it is a bit less convenient to do the extension manipulation or run multiple commands with it  Calling multiple commands through xargs  Parallel linking was asked at  Can gcc use multiple cores when linking   TODO  I think I read somewhere that compilation can be reduced to matrix multiplication  so maybe it is also possible to speed up single file compilation for large files  But I can t find a reference now   Tested in Ubuntu 18 10

User · Answer

make will do this for you   Investigate the -j and -l switches in the man page   I don t think g   is parallelizable

User · Answer

You can do this with make - with gnu make it is the -j flag  this will also help on a uniprocessor machine    For example if you want 4 parallel jobs from make   make -j 4   You can also run gcc in a pipe with   gcc -pipe   This will pipeline the compile stages  which will also help keep the cores busy   If you have additional machines available too  you might check out distcc  which will farm compiles out to those as well

User · Answer

People have mentioned make but bjam also supports a similar concept   Using bjam -jx instructs bjam to build up to x concurrent commands   We use the same build scripts on Windows and Linux and using this option halves our build times on both platforms   Nice

User · Answer

There is no such flag  and having one runs against the Unix philosophy of having each tool perform just one function and perform it well  Spawning compiler processes is conceptually the job of the build system  What you are probably looking for is the -j  jobs  flag to GNU make  a la  make -j4  Or you can use pmake or similar parallel make systems

User · Answer

make will do this for you   Investigate the -j and -l switches in the man page   I don t think g   is parallelizable

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