Merge commit '2cd20b72ed3565ac6935911ca0d9b5d73ae70d0d' into concedo_experimental

# Conflicts:
#	CONTRIBUTING.md
#	docs/backend/CANN.md
#	docs/backend/SYCL.md
#	docs/backend/snapdragon/README.md
#	docs/backend/snapdragon/windows.md
#	docs/build.md
#	docs/multimodal/MobileVLM.md
#	docs/ops.md
#	docs/ops/WebGPU.csv
#	examples/debug/README.md
#	examples/llama.vim
#	examples/model-conversion/README.md
#	examples/sycl/README.md
#	ggml/src/ggml-cpu/amx/mmq.cpp
#	ggml/src/ggml-cpu/arch/x86/repack.cpp
#	ggml/src/ggml-hexagon/ggml-hexagon.cpp
#	ggml/src/ggml-hexagon/htp-drv.cpp
#	ggml/src/ggml-hexagon/htp/flash-attn-ops.c
#	ggml/src/ggml-hexagon/htp/hvx-base.h
#	ggml/src/ggml-hexagon/htp/hvx-copy.h
#	ggml/src/ggml-hexagon/htp/hvx-inverse.h
#	ggml/src/ggml-hexagon/htp/hvx-reduce.h
#	ggml/src/ggml-hexagon/htp/matmul-ops.c
#	ggml/src/ggml-hexagon/htp/rope-ops.c
#	ggml/src/ggml-hexagon/htp/worker-pool.c
#	ggml/src/ggml-opencl/ggml-opencl.cpp
#	ggml/src/ggml-opencl/kernels/cpy.cl
#	ggml/src/ggml-sycl/common.hpp
#	ggml/src/ggml-sycl/quants.hpp
#	ggml/src/ggml-sycl/softmax.cpp
#	ggml/src/ggml-vulkan/CMakeLists.txt
#	ggml/src/ggml-webgpu/ggml-webgpu-shader-lib.hpp
#	ggml/src/ggml-webgpu/ggml-webgpu.cpp
#	scripts/pr2wt.sh
#	scripts/server-bench.py
#	scripts/snapdragon/windows/run-cli.ps1
#	tests/test-alloc.cpp
#	tests/test-backend-ops.cpp
#	tests/test-chat.cpp
#	tools/cli/cli.cpp
#	tools/completion/README.md
#	tools/cvector-generator/cvector-generator.cpp
#	tools/imatrix/README.md
#	tools/perplexity/README.md
#	tools/server/public_simplechat/readme.md
#	tools/server/tests/README.md

ggml/src/ggml-backend.cpp

@@ -1462,6 +1462,10 @@ static enum ggml_status ggml_backend_sched_compute_splits(ggml_backend_sched_t s
         int split_backend_id = split->backend_id;
         ggml_backend_t split_backend = sched->backends[split_backend_id];
 
+        if (sched->events[split_backend_id][sched->cur_copy] == NULL) {
+            ggml_backend_synchronize(split_backend);
+        }
+
         // copy the input tensors to the split backend
         for (int input_id = 0; input_id < split->n_inputs; input_id++) {
             ggml_backend_t input_backend = ggml_backend_sched_get_tensor_backend(sched, split->inputs[input_id]);
@@ -1472,16 +1476,12 @@ static enum ggml_status ggml_backend_sched_compute_splits(ggml_backend_sched_t s
                 // inputs from the user must be copied immediately to prevent the user overwriting the data before the copy is done
                 if (sched->events[split_backend_id][sched->cur_copy] != NULL) {
                     ggml_backend_event_synchronize(sched->events[split_backend_id][sched->cur_copy]);
-                } else {
-                    ggml_backend_synchronize(split_backend);
                 }
-                ggml_backend_tensor_copy(input, input_cpy);
+                ggml_backend_tensor_copy_async(input_backend, split_backend, input, input_cpy);
             } else {
                 // wait for the split backend to finish using the input before overwriting it
                 if (sched->events[split_backend_id][sched->cur_copy] != NULL) {
                     ggml_backend_event_wait(split_backend, sched->events[split_backend_id][sched->cur_copy]);
-                } else {
-                    ggml_backend_synchronize(split_backend);
                 }
 
                 // when offloading MoE weights, we can reduce the amount of data copied by copying only the experts that are used
@@ -1585,6 +1585,10 @@ static enum ggml_status ggml_backend_sched_compute_splits(ggml_backend_sched_t s
             }
         }
 
+        if (sched->events[split_backend_id][sched->cur_copy] == NULL) {
+            ggml_backend_synchronize(split_backend);
+        }
+
         if (!sched->callback_eval) {
             enum ggml_status ec = ggml_backend_graph_compute_async(split_backend, &split->graph);
             if (ec != GGML_STATUS_SUCCESS) {