[petsc-users] Pthread support

[Barry Smith]

On Jul 24, 2012, at 2:06 PM, Jed Brown wrote:

> On Tue, Jul 24, 2012 at 1:59 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> But how do you know what cores the other processes on the machine are using? Couldn't they be anything?
> 
> Yes, but a person running a single-process multi-thread job should be doing something like (suppose a 32-core machine)
> 
> $ taskset 0x000000ff ./job1 -nthreads 8     # use all slots
> $ taskset 0xffffff00 ./job2 -nthreads 12    # use 12 of 24 "slots" arbitrarily


    Cool. Do we have properly documented in the FAQ or some place how the user should be running things with MPICH, OpenMPI etc etc.   This issue is going to keep coming up and my rather useless response can be "yikes, I don't know, look at xxxx".

    Thanks

    Barry

> 
> 
> Now the second job might set affinity by splitting the 24 slots between the 12 threads, or it might group them into three groups per CPU die, setting 0xff00000000, 0x00ff0000, and 0x0000ff00 for all four threads in each of the three groups respectively.