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metal : fix fusion across different encoders #14849

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Merged
merged 2 commits into from
Jul 24, 2025
Merged

metal : fix fusion across different encoders #14849

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d28be8b
metal : fix fusion across different encoders
ggerganov Jul 24, 2025
42826eb
cont : add assertion
ggerganov Jul 24, 2025
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13 changes: 10 additions & 3 deletions ggml/src/ggml-metal/ggml-metal.m
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Original file line number Diff line number Diff line change
Expand Up @@ -1955,6 +1955,7 @@ static bool ggml_metal_supports_op(const struct ggml_backend_metal_device_contex
static int ggml_metal_encode_node(
ggml_backend_t backend,
int idx,
int idx_end,
id<MTLComputeCommandEncoder> encoder,
struct ggml_metal_mem_pool * mem_pool) {
struct ggml_backend_metal_context * ctx = backend->context;
Expand Down Expand Up @@ -2181,7 +2182,9 @@ static int ggml_metal_encode_node(
size_t offs_fuse;
id<MTLBuffer> id_fuse;

for (n_fuse = 0; n_fuse <= 6; ++n_fuse) {
// note: in metal, we sometimes encode the graph in parallel so we have to avoid fusing nodes
// across splits. idx_end indicates the last node in the current split
for (n_fuse = 0; n_fuse <= 6 && idx + n_fuse + 1 < idx_end; ++n_fuse) {
if (!ggml_can_fuse(gf, idx + n_fuse, ops + n_fuse, 2)) {
break;
}
Expand Down Expand Up @@ -4288,7 +4291,7 @@ static int ggml_metal_encode_node(
ops[1] = GGML_OP_MUL;
ops[2] = GGML_OP_ADD;

for (n_fuse = 0; n_fuse <= 1; ++n_fuse) {
for (n_fuse = 0; n_fuse <= 1 && idx + n_fuse + 1 < idx_end; ++n_fuse) {
if (!ggml_can_fuse(gf, idx + n_fuse, ops + n_fuse, 2)) {
break;
}
Expand Down Expand Up @@ -6271,7 +6274,11 @@ static void ggml_backend_metal_set_n_cb(ggml_backend_t backend, int n_cb) {
[encoder pushDebugGroup:[NSString stringWithCString:ggml_op_desc(ggml_graph_node(ctx->gf, idx)) encoding:NSUTF8StringEncoding]];
}

const int res = ggml_metal_encode_node(backend, idx, encoder, mem_pool);
const int res = ggml_metal_encode_node(backend, idx, node_end, encoder, mem_pool);
if (idx + res > node_end) {
GGML_ABORT("fusion error: nodes spanning multiple encoders have been fused. this indicates a bug in the fusion logic %s",
"https://github.com/ggml-org/llama.cpp/pull/14849");
}

if (should_capture) {
[encoder popDebugGroup];
Expand Down
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