Few fixes.

* prevent clearing c_thread_buffer between consecutive k-dim data tiles GEMM.
* Limit the number of launched thread blocks.

include/ck/tensor_operation/gpu/device/impl/device_grouped_gemm_multiple_d_splitk_xdl_cshuffle_tile_loop.hpp

@@ -89,7 +89,9 @@ __global__ void
 
     // early exit if no work.
     if(work_scheduler.tile_id_ >= tile_count)
+    {
         return;
+    }
 
     index_t group_id = 0;
     index_t offset   = 0;
@@ -101,6 +103,7 @@ __global__ void
 
     index_t gemm_tile_id_start = 0;
     index_t gemm_tile_id_end   = grid_size_grp;
+    auto gridwise_gemm         = GridwiseGemm();
 
     do
     {
@@ -127,11 +130,13 @@ __global__ void
         const auto StrideA = gemm_desc_ptr[group_id].StrideA;
         const auto StrideB = gemm_desc_ptr[group_id].StrideB;
 
-        auto gridwise_gemm = GridwiseGemm();
+        auto& results_buffer = gridwise_gemm.GetCThreadBuffer();
         b2c_tile_map.CalculateBottomIndex(work_scheduler.tile_id_ - offset);
+        results_buffer.Clear();
 
         // Iterate over K dimension for this [M,N] tile
         // still in the same GEMM && the same [M,N] tile
+        // TODO: change desc so that few K-tiles will be done in single GEMM.
         do
         {
             // just accumulate results in registers!
@@ -211,7 +216,6 @@ __global__ void
         }
         else if(work_scheduler.HasTile())
         {
-            // TODO: double buffering in order to not wait for this.
             work_scheduler.WaitForReduction(k_batch, output_tile_idx, output_tile_idx_offset);
         }
     } while(work_scheduler.HasTile());
@@ -747,9 +751,17 @@ struct DeviceGroupedGemmMultipleDSplitKXdlCShuffle
             // configuration the first is smaller than the latter. Launching too many workgroups
             // mean some of them will have to iterate through all gemm problem descriptors just to
             // find out they have nothing to do which is of course waste of GPU cycles.
-            const index_t grid_size       = ck::math::min(arg.tile_count_, max_occupancy_grid_size);
+            index_t grid_size             = ck::math::min(arg.tile_count_, max_occupancy_grid_size);
             const index_t tiles_per_block = (arg.tile_count_ + grid_size - 1) / grid_size;
 
+            // Make a correction to grid size in order to get rid of workgroups which does not have
+            // anything to work.
+            if(arg.tile_count_ > max_occupancy_grid_size &&
+               grid_size * tiles_per_block > arg.tile_count_)
+            {
+                grid_size = (arg.tile_count_ + tiles_per_block - 1) / tiles_per_block;
+            }
+
             std::size_t acc_workspace_size_bytes = Block2ETileMapKSplit::GetAccWorkspaceSize(
                 sizeof(typename GridwiseGemm::AccType), grid_size);
 
@@ -774,11 +786,10 @@ struct DeviceGroupedGemmMultipleDSplitKXdlCShuffle
             };
 
             return launch_and_time_kernel_with_preprocess(
-                // return launch_and_time_kernel(
                 stream_config,
                 preprocess,
                 kernel,
-                dim3(ck::math::min(arg.tile_count_, max_occupancy_grid_size)),
+                dim3(grid_size),
                 dim3(BlockSize),
                 0,
                 cast_pointer_to_constant_address_space(dev_gemm_args),

include/ck/tensor_operation/gpu/grid/gridwise_gemm_multiple_d_xdl_splitk_cshuffle_v2.hpp

@@ -754,6 +754,8 @@ class GridwiseGemmMultipleD_xdl_splitk_cshuffle_v2
                                             a_grid_desc_kbatch_ak0_m_ak1.GetLength(I3)) /
                                            KPerBlock);
 
+        bool clear_c_thread_buf = false;
+
         gridwise_gemm_pipeline.template Run<HasMainKBlockLoop>(a_grid_desc_kbatch_ak0_m_ak1,
                                                                a_block_desc_kbatch_ak0_m_ak1,
                                                                a_blockwise_copy,
@@ -768,7 +770,8 @@ class GridwiseGemmMultipleD_xdl_splitk_cshuffle_v2
                                                                b_block_slice_copy_step,
                                                                blockwise_gemm_,
                                                                c_thread_buf,
-                                                               num_k_block_main_loop);
+                                                               num_k_block_main_loop,
+                                                               clear_c_thread_buf);
     }
 
     template <bool HasMainKBlockLoop, typename Block2ETileMap>

include/ck/tensor_operation/gpu/grid/gridwise_gemm_pipeline_v1.hpp

@@ -55,7 +55,8 @@ struct GridwiseGemmPipeline_v1<1>
                                const BBlockTransferStep& b_block_copy_step,
                                const BlockwiseGemm& blockwise_gemm,
                                CThreadBuffer& c_thread_buf,
-                               index_t num_loop)
+                               index_t num_loop,
+                               bool clear_c_thread_buf = true)
     {
         // preload data into LDS
         a_blockwise_copy.RunRead(a_grid_desc, a_grid_buf);
@@ -65,6 +66,7 @@ struct GridwiseGemmPipeline_v1<1>
         b_blockwise_copy.MoveSrcSliceWindow(b_grid_desc, b_block_copy_step);
 
         // Initialize C
+        if(clear_c_thread_buf)
             c_thread_buf.Clear();
 
         a_blockwise_copy.RunWrite(a_block_desc, a_block_buf);

include/ck/utility/work_scheduling.hpp

@@ -93,7 +93,6 @@ class StridedReductionTileLoop
     FlagFinished(index_t k_tiles, index_t output_tile_idx, index_t output_tile_idx_offset)
     {
         const auto fidx = GetWorkgroupFlagIdx(k_tiles, output_tile_idx, output_tile_idx_offset);
-
         finished_block_flags_.inc(fidx);
     }