Groups   9 of 99+      julia-users › Too many processes for non-parallel Julia computation 12 posts by 5 authors      Jorge Fernández de Cossío Díaz    May 5   In my system, running julia from the console to launch the REPL launches 3 processes named Julia. If I execute a julia script containing no parallel code, like  julia myscript-jl  I also get 3 processes, and all three seem to do work.  I have NOT aliased julia to julia -p 3.  I am using Ubuntu 15.10, although this also happens on a system with 14.04, and on a remote cluster, and with different scripts. All are x64, Julia v0.4.5. In all cases, too many processes are launched.  Any ideas on what could be happening?     James Fairbanks    May 5   If you don't run a script, do the other process still do work? I also get multiple julia processes on ubuntu 15.10 juliav0.4.5 but they are all quiet if no script is executed.      Jorge Fernández de Cossío Díaz    May 5   nprocs   returns 1.  I just tried this on an 8-core machine  Intel i7 quad-core with hyperthreading . Executing julia on the console to open the REPL spawns 8 processes.     Penn Taylor    May 5    How are you determining the number of processes?  On Ubuntu 15.04 with Julia v0.4.5, I see  one  process if I issue  $ ps ax | grep julia  But I see 4 process if I look at the process table in `htop`. Htop reports threads as processes though, so this is really a single process with 4 threads. Is this perhaps what you're seeing?     James Fairbanks    May 5  Re:  julia-users  Re: Too many processes for non-parallel Julia computation  This is my circumstance as well. ps ax shows 1  process  htop shows ncores  threads .      Yichao Yu    May 5    Those should be OpenBLAS worker thread and should not cost you any  trouble unless you are hitting the PID limit.      Jorge Fernández de Cossío Díaz    May 5   No, they are quiet. Running a script though causes all the threads to do work.   On Thursday, May 5, 2016 at 4:02:05 PM UTC-4, James Fairbanks wrote: If you don't run a script, do the other process still do work? I also get multiple julia processes on ubuntu 15.10 juliav0.4.5 but they are all quiet if no script is executed.      Jorge Fernández de Cossío Díaz    May 5   You're right, I mean threads, not processes.      Jorge Fernández de Cossío Díaz    May 5   If I run a julia script on a cluster, should I request more than one process?  My calculation is not parallel       James Fairbanks    May 5   If the code is not parallel, then you should not request multiple processors. The builtin BLAS are set up for multiple threads by default.  If you are doing a lot of linear algebra, then that will be parallel already. If you do julia -p then the BLAS are in serial.  James      Jorge Fernández de Cossío Díaz    May 6   I am doing linear algebra. So if I want to force serial computation, I should do julia -p 1 myscript-jl? Will try this next week and let you know.  I don't access to the cluster now . Thanks.      Chris Rackauckas    May 6   No, -p 0 makes there be no worker processes which is the default, but that won't change the linear algebra threads. Instead, if you want to have BLAS use 1 thread, use blas_set_num_threads 1 .