Commit 190a1114 authored by Ethan Stewart's avatar Ethan Stewart Committed by JonChesterfield
Browse files

Changed omp_get_max_threads() implementation to more closely match spec description. 

Summary: The 5.0 spec states, "The omp_get_max_threads routine returns an upper bound on the number of threads that could be used to form a new team if a parallel construct without a num_threads clause were encountered after execution returns from this routine." The attached test shows Max Threads: 96, Num Threads: 128 without the proposed change. The number of threads should not exceed the (max) nthreads ICV, hence we should return the higher SPMD thread number even when omp_get_max_threads() is called in a generic kernel. This change does fail the api test, max_threads.c, because now it would return 64 instead of 32.

Reviewers: jdoerfert, ABataev, grokos, JonChesterfield

Reviewed By: jdoerfert

Subscribers: openmp-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D74092
parent c2ce9ea4

openmp/libomptarget/deviceRTLs/common/src/omptarget.cu

+1 −1
Original line number Diff line number Diff line
@@ -68,7 +68,7 @@ EXTERN void __kmpc_kernel_init(int ThreadLimit, int16_t RequiresOMPRuntime) { 
  // set number of threads and thread limit in team to started value

  omptarget_nvptx_TaskDescr *currTaskDescr =

      omptarget_nvptx_threadPrivateContext->GetTopLevelTaskDescr(threadId);

  nThreads = GetNumberOfWorkersInTeam();

  nThreads = GetNumberOfThreadsInBlock();

  threadLimit = ThreadLimit;

}

openmp/libomptarget/deviceRTLs/nvptx/test/api/get_max_threads.c

0 → 100644
+22 −0
Original line number Diff line number Diff line 
// RUN: %compile-run-and-check

#include <omp.h>

#include <stdio.h>



int main(){

  int max_threads = -1;

  int num_threads = -1;



  #pragma omp target map(tofrom: max_threads)

    max_threads = omp_get_max_threads();



  #pragma omp target parallel map(tofrom: num_threads)

  {

    #pragma omp master

      num_threads = omp_get_num_threads();

  }

  

  // CHECK: Max Threads: 128, Num Threads: 128

  printf("Max Threads: %d, Num Threads: %d\n", max_threads, num_threads);



  return 0;

}

openmp/libomptarget/deviceRTLs/nvptx/test/api/max_threads.c

+8 −1
Original line number Diff line number Diff line
@@ -19,7 +19,14 @@ int main(int argc, char *argv[]) { 
    { MaxThreadsL2 = omp_get_max_threads(); }

  }



  // CHECK: Non-SPMD MaxThreadsL1 = 32

  //FIXME: This Non-SPMD kernel will have 32 active threads due to

  //       thread_limit. However, Non-SPMD MaxThreadsL1 is the total number of

  //       threads in block (64 in this case), which translates to worker

  //       threads + WARP_SIZE for Non-SPMD kernels and worker threads for SPMD

  //       kernels. According to the spec, omp_get_max_threads must return the

  //       max active threads possible between the two kernel types.



  // CHECK: Non-SPMD MaxThreadsL1 = 64

  printf("Non-SPMD MaxThreadsL1 = %d\n", MaxThreadsL1);

  // CHECK: Non-SPMD MaxThreadsL2 = 1

  printf("Non-SPMD MaxThreadsL2 = %d\n", MaxThreadsL2);