diff --git a/ggml/src/ggml-backend.cpp b/ggml/src/ggml-backend.cpp index a3574e914f..26580720dd 100644 --- a/ggml/src/ggml-backend.cpp +++ b/ggml/src/ggml-backend.cpp @@ -11,10 +11,6 @@ #include "ggml-backend.h" #include "ggml-backend-impl.h" #include "ggml-alloc.h" -#include "ggml-cpu.h" -#ifdef GGML_CUDA -#include "ggml-cuda.h" -#endif // GGML_CUDA #include "ggml-impl.h" #include @@ -740,22 +736,38 @@ struct ggml_backend_sched { int debug_prev_graph_size; }; -static void ggml_backend_synchronize_if_required(ggml_backend_t current_backend) { - // TODO add env-flag check here to auto-disable this change +static void ggml_backend_synchronize_if_required(ggml_backend_t current_backend, bool backend_implicitly_synced) { -#ifdef GGML_CUDA - // CUDA backends have an implicit order between execution and memory operations via the CUDA stream. - // Multiple parallel copies are also possible. - // There is consequently no need to synchronize in between computation and subsequent memcpys - if (ggml_backend_is_cuda(current_backend)) { + if (backend_implicitly_synced) { return; } -#endif // GGML_CUDA - // in all other cases, just sync. ggml_backend_synchronize(current_backend); } +static bool ggml_backend_implicitly_synced(ggml_backend_t current_backend) { + /* + * Some backends have implicit synchronization mechanisms, which allows several parallel asynchronous memory copies without data races. + * An example for that is the CUDA backend with the CUDA stream. + * For these backends, we can skip costly explicit synchronizations during compute split scheduling. + */ + + static bool disable_scheduler_sync_opt = (getenv("GGML_SCHED_DISABLE_SYNC_OPT") != nullptr); + + if (disable_scheduler_sync_opt) { + return false; + } + + // To not change any APIs or change what ggml-base links to, we can only detect backends by string matching + auto backend_name = ggml_backend_name(current_backend); + if (strncmp(backend_name, "CUDA", 4) == 0) { + return true; + } + + // sync other backends to ensure correctness + return false; +} + #define hash_id(tensor) ggml_hash_find_or_insert(&sched->hash_set, tensor) #define tensor_backend_id(tensor) sched->hv_tensor_backend_ids[hash_id(tensor)] #define tensor_id_copy(id, backend_id, copy_id) sched->hv_tensor_copies[(id) * sched->n_backends * sched->n_copies + (backend_id) * sched->n_copies + (copy_id)] @@ -1472,6 +1484,8 @@ static enum ggml_status ggml_backend_sched_compute_splits(ggml_backend_sched_t s struct ggml_backend_sched_split * split = &splits[split_id]; int split_backend_id = split->backend_id; ggml_backend_t split_backend = sched->backends[split_backend_id]; + // some backends can avoid costly syncs between async copies + bool backend_implicitly_synced = ggml_backend_implicitly_synced(split_backend); // copy the input tensors to the split backend for (int input_id = 0; input_id < split->n_inputs; input_id++) { @@ -1484,16 +1498,16 @@ 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_event_synchronize(sched->events[split_backend_id][sched->cur_copy]); } else { - ggml_backend_synchronize_if_required(split_backend); + ggml_backend_synchronize_if_required(split_backend, backend_implicitly_synced); } ggml_backend_tensor_copy_async(input_backend, split_backend, input, input_cpy); - ggml_backend_synchronize_if_required(split_backend); + ggml_backend_synchronize_if_required(split_backend, backend_implicitly_synced); } 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_if_required(split_backend); + ggml_backend_synchronize_if_required(split_backend, backend_implicitly_synced); } // when offloading MoE weights, we can reduce the amount of data copied by copying only the experts that are used