[OPENMP][NVPTX]Improve number of threads counter, NFC.

[ABataev]

Summary

Patch improves performance of the full runtime mode by moving
number-of-threads counter to the shared memory. It also allows to save
global memory.

[grokos]

Looks good.

libomptarget/deviceRTLs/nvptx/src/libcall.cu

33–36

Can you make this comment clearer? What is the first parallel region and what are the other parallel regions? I suppose you mean L1 parallel vs nested?

[ABataev]

Updated comment

[ABataev]

There was another patch instead of this one.

libomptarget/deviceRTLs/nvptx/src/libcall.cu

EXTERN double omp_get_wtime(void) {
   unsigned long long nsecs;
   asm("mov.u64  %0, %%globaltimer;" : "=l"(nsecs));
   double rc = (double)nsecs * TIMER_PRECISION;
   PRINT(LD_IO, "call omp_get_wtime() returns %g\n", rc);
   return rc;
 }
 
 EXTERN void omp_set_num_threads(int num) {
-  // Ignore it for SPMD mode.
-  if (isSPMDMode())
+  // Ignore it if the parallel region is started already, inner L2+ parallel
+  // regions can have only 1 thread maximum.
+  if (parallelLevel[GetWarpId()] > 0)
     return;
   ASSERT0(LT_FUSSY, isRuntimeInitialized(), "Expected initialized runtime.");
   PRINT(LD_IO, "call omp_set_num_threads(num %d)\n", num);
   if (num <= 0) {
     WARNING0(LW_INPUT, "expected positive num; ignore\n");
   } else {
-    omptarget_nvptx_TaskDescr *currTaskDescr =
-        getMyTopTaskDescriptor(/*isSPMDExecutionMode=*/false);
-    currTaskDescr->NThreads() = num;
+    numberOfThreads = num;
   }
 }
 
 EXTERN int omp_get_num_threads(void) {
   bool isSPMDExecutionMode = isSPMDMode();
   int tid = GetLogicalThreadIdInBlock(isSPMDExecutionMode);
   int rc = GetNumberOfOmpThreads(tid, isSPMDExecutionMode);
   PRINT(LD_IO, "call omp_get_num_threads() return %d\n", rc);
   return rc;
 }
 
 EXTERN int omp_get_max_threads(void) {
   if (parallelLevel[GetWarpId()] > 0)
     // We're already in parallel region.
     return 1; // default is 1 thread avail
-  omptarget_nvptx_TaskDescr *currTaskDescr =
-      getMyTopTaskDescriptor(/*isSPMDExecutionMode=*/false);
-  ASSERT0(LT_FUSSY, !currTaskDescr->InParallelRegion(),
-          "Should no be in the parallel region");
-  // Not currently in a parallel region, return what was set.
-  int rc = currTaskDescr->NThreads();
+  int rc = numberOfThreads;
   ASSERT0(LT_FUSSY, rc >= 0, "bad number of threads");
   PRINT(LD_IO, "call omp_get_max_threads() return %d\n", rc);
   return rc;
 }
 
 EXTERN int omp_get_thread_limit(void) {
   if (isSPMDMode())
     return GetNumberOfThreadsInBlock();
if (level <= totLevel) {
                 "task descr %s %d: %s, in par %d, rt sched %d,"
                 " chunk %" PRIu64 "; tid %d, tnum %d, nthreads %d\n",
                 "ancestor", steps,
                 (currTaskDescr->IsParallelConstruct() ? "par" : "task"),
                 (int)currTaskDescr->InParallelRegion(), (int)sched,
                 currTaskDescr->RuntimeChunkSize(),
                 (int)currTaskDescr->ThreadId(),
                 (int)currTaskDescr->ThreadsInTeam(),
-                (int)currTaskDescr->NThreads());
+                (int)numberOfThreads);
         }
 
         if (currTaskDescr->IsParallelConstruct()) {
           // found the level
           if (!steps) {
             rc = currTaskDescr->ThreadId();
             break;
           }

libomptarget/deviceRTLs/nvptx/src/omp_data.cu

omptarget_nvptx_Queue<omptarget_nvptx_ThreadPrivateContext, OMP_STATE_COUNT>
         omptarget_nvptx_device_State[MAX_SM];
 
 __device__ omptarget_nvptx_SimpleMemoryManager
     omptarget_nvptx_simpleMemoryManager;
 __device__ __shared__ uint32_t usedMemIdx;
 __device__ __shared__ uint32_t usedSlotIdx;
 
 __device__ __shared__ uint8_t parallelLevel[MAX_THREADS_PER_TEAM / WARPSIZE];
+__device__ __shared__ uint16_t numberOfThreads;
 
 // Pointer to this team's OpenMP state object
 __device__ __shared__
     omptarget_nvptx_ThreadPrivateContext *omptarget_nvptx_threadPrivateContext;
 
 ////////////////////////////////////////////////////////////////////////////////
 // The team master sets the outlined parallel function in this variable to
 // communicate with the workers.  Since it is in shared memory, there is one

libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h

public:
   INLINE int InL2OrHigherParallelRegion() const {
     return items.flags & TaskDescr_InParL2P;
   }
   INLINE int IsParallelConstruct() const {
     return items.flags & TaskDescr_IsParConstr;
   }
   INLINE int IsTaskConstruct() const { return !IsParallelConstruct(); }
   // methods for other fields
-  INLINE uint16_t &NThreads() { return items.nthreads; }
   INLINE uint16_t &ThreadLimit() { return items.threadlimit; }
   INLINE uint16_t &ThreadId() { return items.threadId; }
   INLINE uint16_t &ThreadsInTeam() { return items.threadsInTeam; }
   INLINE uint64_t &RuntimeChunkSize() { return items.runtimeChunkSize; }
   INLINE omptarget_nvptx_TaskDescr *GetPrevTaskDescr() const { return prev; }
   INLINE void SetPrevTaskDescr(omptarget_nvptx_TaskDescr *taskDescr) {
     prev = taskDescr;
   }
struct SavedLoopDescr_items {
     int64_t chunk;
     int64_t stride;
     kmp_sched_t schedule;
   } loopData;
 
   struct TaskDescr_items {
     uint8_t flags; // 6 bit used (see flag above)
     uint8_t unused;
-    uint16_t nthreads;         // thread num for subsequent parallel regions
     uint16_t threadlimit;      // thread limit ICV
     uint16_t threadId;         // thread id
     uint16_t threadsInTeam;    // threads in current team
     uint64_t runtimeChunkSize; // runtime chunk size
   } items;
   omptarget_nvptx_TaskDescr *prev;
 };
 

 ////////////////////////////////////////////////////////////////////////////////
 
 extern __device__ omptarget_nvptx_SimpleMemoryManager
     omptarget_nvptx_simpleMemoryManager;
 extern __device__ __shared__ uint32_t usedMemIdx;
 extern __device__ __shared__ uint32_t usedSlotIdx;
 extern __device__ __shared__ uint8_t
     parallelLevel[MAX_THREADS_PER_TEAM / WARPSIZE];
+extern __device__ __shared__ uint16_t numberOfThreads;
 extern __device__ __shared__
     omptarget_nvptx_ThreadPrivateContext *omptarget_nvptx_threadPrivateContext;
 
 extern __device__ __shared__ uint32_t execution_param;
 extern __device__ __shared__ void *ReductionScratchpadPtr;
 
 ////////////////////////////////////////////////////////////////////////////////
 // work function (outlined parallel/simd functions) and arguments.

libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.cu

EXTERN void __kmpc_kernel_init(int ThreadLimit, int16_t RequiresOMPRuntime) {
   // to point to the level zero task ICV. That ICV was init in
   // InitTeamDescr()
   omptarget_nvptx_threadPrivateContext->SetTopLevelTaskDescr(
       threadId, currTeamDescr.LevelZeroTaskDescr());
 
   // set number of threads and thread limit in team to started value
   omptarget_nvptx_TaskDescr *currTaskDescr =
       omptarget_nvptx_threadPrivateContext->GetTopLevelTaskDescr(threadId);
-  currTaskDescr->NThreads() = GetNumberOfWorkersInTeam();
+  numberOfThreads = GetNumberOfWorkersInTeam();
   currTaskDescr->ThreadLimit() = ThreadLimit;
 }
 
 EXTERN void __kmpc_kernel_deinit(int16_t IsOMPRuntimeInitialized) {
   PRINT0(LD_IO, "call to __kmpc_kernel_deinit\n");
   ASSERT0(LT_FUSSY, IsOMPRuntimeInitialized,
           "Generic always requires initialized runtime.");
   // Enqueue omp state object for use by another team.

libomptarget/deviceRTLs/nvptx/src/omptarget-nvptxi.h

 omptarget_nvptx_TaskDescr::InitLevelZeroTaskDescr(bool isSPMDExecutionMode) {
   // slow method
   // flag:
   //   default sched is static,
   //   dyn is off (unused now anyway, but may need to sample from host ?)
   //   not in parallel
 
   items.flags = 0;
-  items.nthreads = GetNumberOfProcsInTeam(isSPMDExecutionMode);
   ;                                // threads: whatever was alloc by kernel
   items.threadId = 0;         // is master
   items.threadsInTeam = 1;    // sequential
   items.runtimeChunkSize = 1; // prefered chunking statik with chunk 1
 }
 
 // This is called when all threads are started together in SPMD mode.
 // OMP directives include target parallel, target distribute parallel for, etc.
 INLINE void omptarget_nvptx_TaskDescr::InitLevelOneTaskDescr(
     uint16_t tnum, omptarget_nvptx_TaskDescr *parentTaskDescr) {
   // slow method
   // flag:
   //   default sched is static,
   //   dyn is off (unused now anyway, but may need to sample from host ?)
   //   in L1 parallel
 
   items.flags =
       TaskDescr_InPar | TaskDescr_IsParConstr; // set flag to parallel
-  items.nthreads = 0; // # threads for subsequent parallel region
   items.threadId =
       GetThreadIdInBlock(); // get ids from cuda (only called for 1st level)
   items.threadsInTeam = tnum;
   items.runtimeChunkSize = 1; // prefered chunking statik with chunk 1
   prev = parentTaskDescr;
 }
 
 INLINE void omptarget_nvptx_TaskDescr::CopyData(

libomptarget/deviceRTLs/nvptx/src/parallel.cu

EXTERN void __kmpc_kernel_prepare_parallel(void *WorkFn,
   if (currTaskDescr->InParallelRegion()) {
     PRINT0(LD_PAR, "already in parallel: go seq\n");
     return;
   }
 
   uint16_t &NumThreadsClause =
       omptarget_nvptx_threadPrivateContext->NumThreadsForNextParallel(threadId);
 
-  uint16_t NumThreads =
-      determineNumberOfThreads(NumThreadsClause, currTaskDescr->NThreads(),
-                               currTaskDescr->ThreadLimit());
+  uint16_t NumThreads = determineNumberOfThreads(
+      NumThreadsClause, numberOfThreads, currTaskDescr->ThreadLimit());
 
   if (NumThreadsClause != 0) {
     // Reset request to avoid propagating to successive #parallel
     NumThreadsClause = 0;
   }
 
   ASSERT(LT_FUSSY, NumThreads > 0, "bad thread request of %d threads",
          (int)NumThreads);
if (threadId < workDescr.WorkTaskDescr()->ThreadsInTeam()) {
     newTaskDescr->CopyFromWorkDescr(workDescr.WorkTaskDescr());
     // install new top descriptor
     omptarget_nvptx_threadPrivateContext->SetTopLevelTaskDescr(threadId,
                                                                newTaskDescr);
     // init private from int value
     PRINT(LD_PAR,
           "thread will execute parallel region with id %d in a team of "
           "%d threads\n",
-          (int)newTaskDescr->ThreadId(), (int)newTaskDescr->NThreads());
+          (int)newTaskDescr->ThreadId(), (int)numberOfThreads);
 
     isActive = true;
     IncParallelLevel(workDescr.WorkTaskDescr()->ThreadsInTeam() != 1);
   }
 
   return isActive;
 }