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sched : fix multiple evaluations of the same graph with pipeline parallelism #14855

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Merged
merged 1 commit into from
Jul 25, 2025
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sched : fix multiple evaluations of the same graph with pipeline parallelism #14855

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13 changes: 8 additions & 5 deletions ggml/src/ggml-backend.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -647,6 +647,7 @@ struct ggml_backend_sched {
// pipeline parallelism support
int n_copies;
int cur_copy;
int next_copy;
ggml_backend_event_t events[GGML_SCHED_MAX_BACKENDS][GGML_SCHED_MAX_COPIES];
struct ggml_tensor * graph_inputs[GGML_SCHED_MAX_SPLIT_INPUTS];
int n_graph_inputs;
Expand Down Expand Up @@ -1433,8 +1434,6 @@ static enum ggml_status ggml_backend_sched_compute_splits(ggml_backend_sched_t s
}
}

sched->cur_copy = (sched->cur_copy + 1) % sched->n_copies;

return GGML_STATUS_SUCCESS;
}

Expand Down Expand Up @@ -1535,10 +1534,10 @@ void ggml_backend_sched_reset(ggml_backend_sched_t sched) {
bool ggml_backend_sched_reserve(ggml_backend_sched_t sched, struct ggml_cgraph * measure_graph) {
GGML_ASSERT((int)sched->hash_set.size >= measure_graph->n_nodes + measure_graph->n_leafs);

ggml_backend_sched_split_graph(sched, measure_graph);

ggml_backend_sched_synchronize(sched);

ggml_backend_sched_split_graph(sched, measure_graph);

if (!ggml_gallocr_reserve_n(sched->galloc, &sched->graph, sched->node_backend_ids, sched->leaf_backend_ids)) {
return false;
}
Expand All @@ -1550,6 +1549,10 @@ bool ggml_backend_sched_reserve(ggml_backend_sched_t sched, struct ggml_cgraph *

bool ggml_backend_sched_alloc_graph(ggml_backend_sched_t sched, struct ggml_cgraph * graph) {
GGML_ASSERT((int)sched->hash_set.size >= graph->n_nodes + graph->n_leafs);
GGML_ASSERT(!sched->is_alloc);

sched->cur_copy = sched->next_copy;
sched->next_copy = (sched->next_copy + 1) % sched->n_copies;

ggml_backend_sched_split_graph(sched, graph);

Expand Down Expand Up @@ -1590,7 +1593,7 @@ void ggml_backend_sched_synchronize(ggml_backend_sched_t sched) {
// if the graph is not already allocated, always use copy 0 after a synchronization
// this ensures that during generation the same copy is used every time,
// which avoids changes in the graph that could cause CUDA or other graphs to be disabled
sched->cur_copy = 0;
sched->next_copy = 0;
}
}

Expand Down
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