wiki:AppMultiThread

Version 23 (modified by davea, 15 years ago) (diff)

--

API for multi-thread apps

Why write a multi-threaded app?

The average number of cores per PC will increase over the next few years, possibly at a faster rate than the average amount of available RAM.

Depending on your application and project, it may be desirable to develop a multi-threaded application. Possible reasons to do this:

  • Your application's memory footprint is large enough that, on some PCs, there's not enough RAM to run a separate copy of the app on each CPU.
  • You want to reduce the turnaround time of your jobs (either because of human factors, or to reduce server occupancy).

You may be able to use OpenMP, or languages like Titanium or Cilk, or libraries of multi-threaded numerical "kernels", to develop a multi-threaded app.

Deploying a multi-threaded app version

BOINC uses the application planning mechanism to coordinate the scheduling of multi-threaded applications.

Suppose you've developed a multi-threaded program, and that it achieves a linear speedup on up to 64 processors, and no additional speedup beyond that. To deploy it:

  • Choose a "planning class" name for the program, say "par16" (see below).
  • Create an app version. Include a file app_plan containing "par16".
  • Link the following function into your scheduler:
    bool app_plan(SCHEDULER_REQUEST& sreq, const char* plan_class, HOST_USAGE& hu) {
        if (!strcmp(plan_class, "par64")) {
            int ncpus, nthreads;
            bool bounded;
    
            get_ncpus(sreq, ncpus, bounded);
            nthreads = ncpus;
            if (nthreads > 64) nthreads = 64;
            hu.avg_ncpus = nthreads;
            hu.max_ncpus = nthreads;
            sprintf(hu.cmdline, "--nthreads %d", nthreads);
            hu.flops = 0.95*sreq.host.p_fpops*nthreads;
            return true;
    
        }
        return false;
    }