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change cpu_buft_list order: ACCEL -> GPU host -> CPU extra -> CPU #12632

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Merged
merged 1 commit into from
Mar 29, 2025
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change cpu_buft_list order: ACCEL -> GPU host -> CPU extra -> CPU #12632

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42 changes: 15 additions & 27 deletions src/llama-model.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -256,7 +256,7 @@ static ggml_backend_buffer_type_t select_weight_buft(const llama_hparams & hpara
return nullptr;
}

// CPU: ACCEL -> CPU extra -> GPU host -> CPU
// CPU: ACCEL -> GPU host -> CPU extra -> CPU
static buft_list_t make_cpu_buft_list(const std::vector<ggml_backend_dev_t> & devices) {
buft_list_t buft_list;

Expand All @@ -272,32 +272,6 @@ static buft_list_t make_cpu_buft_list(const std::vector<ggml_backend_dev_t> & de
}
}

bool has_gpu_device = false;
for (auto * dev : devices) {
if (ggml_backend_dev_type(dev) == GGML_BACKEND_DEVICE_TYPE_GPU) {
has_gpu_device = true;
break;
}
}

// add extra buffer types, only if no GPU device is present
// ref: https://github.com/ggml-org/llama.cpp/issues/12481#issuecomment-2743136094
if (!has_gpu_device) {
auto * cpu_dev = ggml_backend_dev_by_type(GGML_BACKEND_DEVICE_TYPE_CPU);
auto * cpu_reg = ggml_backend_dev_backend_reg(cpu_dev);
auto ggml_backend_dev_get_extra_bufts_fn = (ggml_backend_dev_get_extra_bufts_t)
ggml_backend_reg_get_proc_address(cpu_reg, "ggml_backend_dev_get_extra_bufts");
if (ggml_backend_dev_get_extra_bufts_fn) {
ggml_backend_buffer_type_t * extra_bufts = ggml_backend_dev_get_extra_bufts_fn(cpu_dev);
while (extra_bufts && *extra_bufts) {
buft_list.emplace_back(cpu_dev, *extra_bufts);
++extra_bufts;
}
}
} else {
LLAMA_LOG_WARN("%s: disabling extra buffer types (i.e. repacking) since a GPU device is available\n", __func__);
}

// add a host buffer type
// storing the tensors in a host buffer is useful when the processing of large batches
// is offloaded to a GPU device, since it reduces the time spent on data transfers
Expand All @@ -312,6 +286,20 @@ static buft_list_t make_cpu_buft_list(const std::vector<ggml_backend_dev_t> & de
}
}

// add extra buffer types, only if no GPU device is present
// ref: https://github.com/ggml-org/llama.cpp/issues/12481#issuecomment-2743136094
auto * cpu_dev = ggml_backend_dev_by_type(GGML_BACKEND_DEVICE_TYPE_CPU);
auto * cpu_reg = ggml_backend_dev_backend_reg(cpu_dev);
auto ggml_backend_dev_get_extra_bufts_fn = (ggml_backend_dev_get_extra_bufts_t)
ggml_backend_reg_get_proc_address(cpu_reg, "ggml_backend_dev_get_extra_bufts");
if (ggml_backend_dev_get_extra_bufts_fn) {
ggml_backend_buffer_type_t * extra_bufts = ggml_backend_dev_get_extra_bufts_fn(cpu_dev);
while (extra_bufts && *extra_bufts) {
buft_list.emplace_back(cpu_dev, *extra_bufts);
++extra_bufts;
}
}

// add the CPU buffer type
for (size_t i = 0; i < ggml_backend_dev_count(); ++i) {
ggml_backend_dev_t dev = ggml_backend_dev_get(i);
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