Use accelerator_for2d and DeviceSegmentedRecude to avoid kernel launch latencies

Grid/lattice/Lattice_slicesum_gpu.h

@@ -6,6 +6,7 @@
 #define gpuMalloc cudaMalloc
 #define gpuMemcpy cudaMemcpy
 #define gpuMemcpyDeviceToHost cudaMemcpyDeviceToHost
+#define gpuMemcpyHostToDevice cudaMemcpyHostToDevice
 #define gpuError_t cudaError_t
 #define gpuSuccess cudaSuccess
 
@@ -16,6 +17,7 @@
 #define gpuMalloc hipMalloc
 #define gpuMemcpy hipMemcpy
 #define gpuMemcpyDeviceToHost hipMemcpyDeviceToHost
+#define gpuMemcpyHostToDevice hipMemcpyHostToDevice
 #define gpuError_t hipError_t
 #define gpuSuccess hipSuccess
 
@@ -49,14 +51,15 @@ template<class vobj> inline void sliceSumGpu(const Lattice<vobj> &Data,std::vect
   int ostride=grid->_ostride[orthogdim];
   Vector<vobj> lvSum(rd); 
   Vector<sobj> lsSum(ld,Zero());                    
-  commVector<vobj> reduction_buffer(e1*e2);
+  commVector<vobj> reduction_buffer(rd*e1*e2);
   ExtractBuffer<sobj> extracted(Nsimd);                  
   
   result.resize(fd);
   for(int r=0;r<rd;r++){
     lvSum[r]=Zero();
   }
-
+  vobj identity;
+  zeroit(identity);
   
   autoView( Data_v, Data, AcceleratorRead);
   auto rb_p = &reduction_buffer[0];
@@ -65,39 +68,59 @@ template<class vobj> inline void sliceSumGpu(const Lattice<vobj> &Data,std::vect
   vobj *d_out;
   size_t temp_storage_bytes = 0;
   size_t size = e1*e2;
-  gpuMalloc(&d_out,rd*sizeof(vobj));
-  gpuError_t gpuErr =gpucub::DeviceReduce::Sum(helperArray, temp_storage_bytes, rb_p,d_out, size, computeStream);
+  std::vector<int> offsets(rd+1,0);
+  for (int i = 0; i < offsets.size(); i++) {
+    offsets[i] = i*size;
+  }
+  int* d_offsets;
+
+  gpuError_t gpuErr = gpuMalloc(&d_out,rd*sizeof(vobj));
+   if (gpuErr != gpuSuccess) {
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during gpuMalloc(1) Error: " << gpuErr <<std::endl;
+  }
+  gpuErr = gpuMalloc(&d_offsets,sizeof(int)*(rd+1));
+   if (gpuErr != gpuSuccess) {
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during gpuMalloc(2) Error: " << gpuErr <<std::endl;
+  }
+  gpuErr = gpuMemcpy(d_offsets,&offsets[0],sizeof(int)*(rd+1),gpuMemcpyHostToDevice);
+  if (gpuErr != gpuSuccess) {
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during gpuMemcpy(1) Error: " << gpuErr <<std::endl;
+  }
+
+  gpuErr = gpucub::DeviceSegmentedReduce::Reduce(helperArray, temp_storage_bytes, rb_p,d_out, rd, d_offsets, d_offsets+1, ::gpucub::Sum(), identity, computeStream);
   if (gpuErr!=gpuSuccess) {
-    std::cout << "Encountered error during cub::DeviceReduce::Sum(1)! Error: " << gpuErr <<std::endl;
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during cub::DeviceReduce::Sum(1)! Error: " << gpuErr <<std::endl;
   }
   
   gpuErr = gpuMalloc(&helperArray,temp_storage_bytes);
   if (gpuErr!=gpuSuccess) {
-    std::cout << "Encountered error during gpuMalloc Error: " << gpuErr <<std::endl;
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during gpuMalloc Error: " << gpuErr <<std::endl;
   }
-  for (int r = 0; r < rd; r++) {
-    //prepare buffer for reduction
-    accelerator_forNB( s,e1*e2, grid->Nsimd(),{ //use non-blocking accelerator_for to avoid syncs (ok because we submit to same computeStream)
-      
-      int n = s / e2;
-      int b = s % e2;
-      int so=r*ostride; // base offset for start of plane 
-      int ss= so+n*stride+b;
 
-      coalescedWrite(rb_p[s], coalescedRead(Data_v[ss]));
+  //prepare buffer for reduction
+  accelerator_for2dNB( s,e1*e2, r,rd, grid->Nsimd(),{ //use non-blocking accelerator_for to avoid syncs (ok because we submit to same computeStream)
+                                                      //use 2d accelerator_for to avoid launch latencies found when looping over rd 
+    int n = s / e2;
+    int b = s % e2;
+    int so=r*ostride; // base offset for start of plane 
+    int ss= so+n*stride+b;
 
-    });
-    
-    //issue reductions in computeStream 
-    gpuErr =gpucub::DeviceReduce::Sum(helperArray, temp_storage_bytes, rb_p, &d_out[r], size, computeStream);
-    if (gpuErr!=gpuSuccess) {
-      std::cout << "Encountered error during cub::DeviceReduce::Sum(2)! Error: " << gpuErr <<std::endl;
-    }
+    coalescedWrite(rb_p[r*e1*e2+s], coalescedRead(Data_v[ss]));
+
+  });
+  
+  //issue reductions in computeStream
+  gpuErr =gpucub::DeviceSegmentedReduce::Reduce(helperArray, temp_storage_bytes, rb_p, d_out, rd, d_offsets, d_offsets+1,::gpucub::Sum(), identity, computeStream);
+  if (gpuErr!=gpuSuccess) {
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during cub::DeviceReduce::Sum(2)! Error: " << gpuErr <<std::endl;
   }
+  
   //sync before copy
   accelerator_barrier();
-  gpuMemcpy(&lvSum[0],d_out,rd*sizeof(vobj),gpuMemcpyDeviceToHost);
-
+  gpuErr = gpuMemcpy(&lvSum[0],d_out,rd*sizeof(vobj),gpuMemcpyDeviceToHost);
+  if (gpuErr!=gpuSuccess) {
+    std::cout << "Lattice_slicesum_gpu.h: Encountered error during gpuMemcpy(2) Error: " << gpuErr <<std::endl;
+  }
   // Sum across simd lanes in the plane, breaking out orthog dir.
   Coordinate icoor(Nd);
 

Grid/perfmon/Tracing.h

@@ -34,7 +34,7 @@ class GridTracer {
 };
 inline void tracePush(const char *name) { roctxRangePushA(name); }
 inline void tracePop(const char *name) { roctxRangePop(); }
-inline int  traceStart(const char *name) { roctxRangeStart(name); }
+inline int  traceStart(const char *name) { return roctxRangeStart(name); }
 inline void traceStop(int ID) { roctxRangeStop(ID); }
 #endif
 

tests/core/Test_sliceSum.cc

@@ -44,8 +44,9 @@ int main (int argc, char ** argv) {
         std::cout <<" sliceSumGpu took "<<tgpu<<" usecs"<<std::endl;
 
     for(int t=0;t<reduction_reference.size();t++){
-
       auto diff = reduction_reference[t]-reduction_result[t];
+      // std::cout << "Difference = " << diff <<std::endl;
+
       assert(abs(TensorRemove(diff)) < 1e-8 );
     }