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llama.cpp
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Simplifies synchronizations to adhere to `saaasg` pattern.

This commit is contained in:
aendk 2026-01-19 17:45:33 +01:00
parent 43f6684f3d
commit 50344142f4
1 changed files with 7 additions and 52 deletions
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59
ggml/src/ggml-backend.cpp
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@ -670,12 +670,6 @@ static bool ggml_is_view_op(enum ggml_op op) {
#define GGML_SCHED_MAX_COPIES 4
#endif
enum ggml_backend_sync_mode {
GGML_SPLIT_SYNC_MODE_EXPLICIT = 0, // splits which require explicit synchronization throughout (default)
GGML_SPLIT_SYNC_MODE_WRITE_READ_BOUNDARY = 1, // splits which require only a single explicit sync between the last write and the first read
GGML_SPLIT_SYNC_MODE_IMPLICIT = 2 // splits which can rely on implicit sync mechanisms of its backend like a queue or stream
};
struct ggml_backend_sched_split {
int backend_id;
int i_start;
@ -684,7 +678,6 @@ struct ggml_backend_sched_split {
int n_inputs;
// graph view of this split
struct ggml_cgraph graph;
enum ggml_backend_sync_mode backend_sync_mode;
};
struct ggml_backend_sched {
@ -743,42 +736,6 @@ struct ggml_backend_sched {
int debug_prev_graph_size;
};
static void ggml_backend_synchronize_if_required(ggml_backend_sched_split * split, ggml_backend_t current_backend, bool is_final_write = 0) {
if (split->backend_sync_mode == GGML_SPLIT_SYNC_MODE_IMPLICIT) {
return;
}
if (split->backend_sync_mode == GGML_SPLIT_SYNC_MODE_WRITE_READ_BOUNDARY && !is_final_write) {
return;
}
ggml_backend_synchronize(current_backend);
}
static void ggml_backend_implicitly_synced(ggml_backend_sched_split * split, 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.
*/
if (split->backend_sync_mode != GGML_SPLIT_SYNC_MODE_EXPLICIT) {
// indicates that this function has already changed the default value, no repeat check necessary
return;
}
// 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) {
split->backend_sync_mode = GGML_SPLIT_SYNC_MODE_IMPLICIT;
return;
}
// retain default explicit synchronization on other backends for correctness
return;
}
#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)]
@ -1496,32 +1453,26 @@ 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];
// determine if backend can avoid costly syncs between HtoD async copies
ggml_backend_implicitly_synced(split, split_backend);
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]);
struct ggml_tensor * input = split->inputs[input_id];
struct ggml_tensor * input_cpy = tensor_copy(input, split_backend_id, sched->cur_copy);
bool last_input = (input_id + 1) == split->n_inputs;
if (input->flags & GGML_TENSOR_FLAG_INPUT) {
// 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_if_required(split, split_backend);
}
ggml_backend_tensor_copy_async(input_backend, split_backend, input, input_cpy);
ggml_backend_synchronize_if_required(split, split_backend, last_input);
} 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, split_backend, last_input);
}
// when offloading MoE weights, we can reduce the amount of data copied by copying only the experts that are used
@ -1625,6 +1576,10 @@ 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) {