Small maybe optimization in Lihgt CSR kernel.

src/TNL/Algorithms/Segments/Kernels/CSRLightKernel.hpp

@@ -29,7 +29,7 @@ template< typename Real,
           typename Reduce,
           typename Keep >
 __global__
-void SpMVCSRLightWithoutAtomic2( OffsetsView offsets,
+void SpMVCSRLight2( OffsetsView offsets,
                                  const Index first,
                                  const Index last,
                                  Fetch fetch,
@@ -66,7 +66,7 @@ template< typename Real,
           typename Reduce,
           typename Keep >
 __global__
-void SpMVCSRLightWithoutAtomic4( OffsetsView offsets,
+void SpMVCSRLight4( OffsetsView offsets,
                                  const Index first,
                                  const Index last,
                                  Fetch fetch,
@@ -105,7 +105,7 @@ template< typename Real,
           typename Reduce,
           typename Keep >
 __global__
-void SpMVCSRLightWithoutAtomic8( OffsetsView offsets,
+void SpMVCSRLight8( OffsetsView offsets,
                                  const Index first,
                                  const Index last,
                                  Fetch fetch,
@@ -145,7 +145,7 @@ template< typename Real,
           typename Reduce,
           typename Keep >
 __global__
-void SpMVCSRLightWithoutAtomic16( OffsetsView offsets,
+void SpMVCSRLight16( OffsetsView offsets,
                                   const Index first,
                                   const Index last,
                                   Fetch fetch,
@@ -253,14 +253,25 @@ void SpMVCSRVector( OffsetsView offsets,
 
    // Reduction
    if( ThreadsPerSegment > 16 )
+   {
       result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result, 16 ) );
-   if( ThreadsPerSegment > 8 )
       result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  8 ) );
-   if( ThreadsPerSegment > 4 )
       result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  4 ) );
-   if( ThreadsPerSegment > 2 )
       result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  2 ) );
-   if( ThreadsPerSegment > 1 )
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  1 ) );
+   } else if( ThreadsPerSegment > 8 ) {
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  8 ) );
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  4 ) );
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  2 ) );
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  1 ) );
+   } else if( ThreadsPerSegment > 4 ) {
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  4 ) );
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  2 ) );
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  1 ) );
+   } else if( ThreadsPerSegment > 2 ) {
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  2 ) );
+      result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  1 ) );
+   } else if( ThreadsPerSegment > 1 )
       result = reduce( result, __shfl_down_sync(0xFFFFFFFF, result,  1 ) );
 
    // Store result
@@ -461,16 +472,16 @@ struct CSRLightKernelreduceSegmentsDispatcher< Index, Device, Fetch, Reduce, Kee
 
 
          /*if (threadsPerSegment == 2)
-            SpMVCSRLightWithoutAtomic2<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
+            SpMVCSRLight2<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
                offsets, first, last, fetch, reduce, keep, zero, grid );
          else if (threadsPerSegment == 4)
-            SpMVCSRLightWithoutAtomic4<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
+            SpMVCSRLight4<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
                offsets, first, last, fetch, reduce, keep, zero, grid );
          else if (threadsPerSegment == 8)
-            SpMVCSRLightWithoutAtomic8<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
+            SpMVCSRLight8<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
                offsets, first, last, fetch, reduce, keep, zero, grid );
          else if (threadsPerSegment == 16)
-            SpMVCSRLightWithoutAtomic16<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
+            SpMVCSRLight16<Real, Index, OffsetsView, Fetch, Reduce, Keep ><<<blocks, threads>>>(
                offsets, first, last, fetch, reduce, keep, zero, grid );
          else if (threadsPerSegment == 32)
          { // CSR SpMV Light with threadsPerSegment = 32 is CSR Vector