These functions are returning the physical placement at the moment they are called. If a Pthread moves around, it will still return the correct, current value.
You should not cache the output of these functions. They require ~105 cycles per call (I just measured this for 1M calls, with 315-318M cycles required for the test), which is cheaper than loading a stored value if it's not in cache. Jeff On Tue, Jan 8, 2013 at 7:50 PM, Erik Schnetter <schnet...@cct.lsu.edu> wrote: > Jeff > > Thanks, this is helpful. I am mostly interested in finding out which threads > share the D1 cache. I guess that get_bgq_core returns this information. > > Is there a way to guarantee that this association doesn't change at run > time? I guess I could just check periodically... > > -erik > > > > On Tue, Jan 8, 2013 at 5:33 PM, Jeff Hammond <jhamm...@alcf.anl.gov> wrote: >> >> As a temporary, non-portable substitute for hwloc, you can use the SPI >> calls that are described on my Wiki: >> https://wiki.alcf.anl.gov/parts/index.php/Blue_Gene/Q#Node_topology. >> I presume that this is the means by which hwloc will support BGQ when >> it does. >> >> Blue Gene/Q has 16+1 cores with 4 hw threads each. Only 16 cores are >> visible to applications but as users can, in theory, run code on the >> 17th core (see >> https://wiki.alcf.anl.gov/parts/index.php/Blue_Gene/Q#17th_Core_App_Agents >> for how), it is important for these functions to return values in the >> range 0..16 and 0..67 instead of 0..15 and 0..63. I include this >> information in case users are confused about the additional range >> documented for these calls. >> >> Best, >> >> Jeff >> >> On Tue, Jan 8, 2013 at 11:10 AM, Brice Goglin <brice.gog...@inria.fr> >> wrote: >> > Hello Erik, >> > We need specific BGQ binding support, the binding API is different. Also >> > we >> > don't properly detect the 16 4-way cores properly, we only only 64 >> > identical >> > PUs. >> > I am supposed to get a BGQ account in the near future so I hope I will >> > have >> > everything working in v1.7. >> > Stay tuned >> > Brice >> > >> > >> > >> > >> > Le 08/01/2013 18:06, Erik Schnetter a écrit : >> > >> > I am trying to use hwloc on a Blue Gene/Q. Building and installing >> > worked >> > fine, and it reports the system configuration fine as well (i.e. it >> > shows >> > all PUs). However, when I try to inquire the thread/core bindings, hwloc >> > crashes with an error in libc's free(). This is both with 1.6 and >> > 1.6.1rc1. >> > >> > The error occurs apparently in CPU_FREE called from >> > hwloc_linux_find_kernel_nr_cpus. >> > >> > Does this ring a bell with anyone? I know this is not enough information >> > to >> > debug things, but do you have any pointers for things to look at? >> > >> > I remember reading somewhere that the last bit in a cpu_set_t cannot be >> > used. A Blue Gene/Q has 64 PUs, and may be using 64-bit integers to hold >> > cpu_set_t data. Could this be an issue? >> > >> > My goal is to examine and experiment with thread/core bindings with >> > OpenMP >> > to improve performance. >> > >> > -erik >> > >> > -- >> > Erik Schnetter <schnet...@gmail.com> >> > http://www.perimeterinstitute.ca/personal/eschnetter/ >> > >> > >> > _______________________________________________ >> > hwloc-users mailing list >> > hwloc-us...@open-mpi.org >> > http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-users >> > >> > >> > >> > _______________________________________________ >> > hwloc-users mailing list >> > hwloc-us...@open-mpi.org >> > http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-users >> >> >> >> -- >> Jeff Hammond >> Argonne Leadership Computing Facility >> University of Chicago Computation Institute >> jhamm...@alcf.anl.gov / (630) 252-5381 >> http://www.linkedin.com/in/jeffhammond >> https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond >> >> _______________________________________________ >> hwloc-users mailing list >> hwloc-us...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-users > > > > > -- > Erik Schnetter <schnet...@cct.lsu.edu> > http://www.perimeterinstitute.ca/personal/eschnetter/ > > _______________________________________________ > hwloc-users mailing list > hwloc-us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-users -- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute jhamm...@alcf.anl.gov / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond
