use a host buffer for the cpu compute buffer for faster copies to the gpu

ggml-alloc.c

@@ -265,9 +265,9 @@ ggml_tallocr_t ggml_tallocr_new_measure(size_t alignment) {
     return alloc;
 }
 
-ggml_tallocr_t ggml_tallocr_new_measure_from_backend(struct ggml_backend * backend) {
+ggml_tallocr_t ggml_tallocr_new_measure_from_buft(struct ggml_backend_buffer_type * buft) {
     // create a backend buffer to get the correct tensor allocation sizes
-    ggml_backend_buffer_t buffer = ggml_backend_alloc_buffer(backend, 1);
+    ggml_backend_buffer_t buffer = ggml_backend_buft_alloc_buffer(buft, 1);
 
     // TODO: move alloc initialization to a common ggml_tallocr_new_impl function
     ggml_tallocr_t alloc = ggml_tallocr_new_from_buffer(buffer);
@@ -277,13 +277,22 @@ ggml_tallocr_t ggml_tallocr_new_measure_from_backend(struct ggml_backend * backe
     return alloc;
 }
 
-ggml_tallocr_t ggml_tallocr_new_from_backend(struct ggml_backend * backend, size_t size) {
-    ggml_backend_buffer_t buffer = ggml_backend_alloc_buffer(backend, size);
+ggml_tallocr_t ggml_tallocr_new_measure_from_backend(struct ggml_backend * backend) {
+    return ggml_tallocr_new_measure_from_buft(ggml_backend_get_default_buffer_type(backend));
+}
+
+ggml_tallocr_t ggml_tallocr_new_from_buft(struct ggml_backend_buffer_type * buft, size_t size) {
+    // create a backend buffer to get the correct tensor allocation sizes
+    ggml_backend_buffer_t buffer = ggml_backend_buft_alloc_buffer(buft, size);
     ggml_tallocr_t alloc = ggml_tallocr_new_from_buffer(buffer);
     alloc->buffer_owned = true;
     return alloc;
 }
 
+ggml_tallocr_t ggml_tallocr_new_from_backend(struct ggml_backend * backend, size_t size) {
+    return ggml_tallocr_new_from_buft(ggml_backend_get_default_buffer_type(backend), size);
+}
+
 ggml_tallocr_t ggml_tallocr_new_from_buffer(struct ggml_backend_buffer * buffer) {
     ggml_tallocr_t alloc = (ggml_tallocr_t)malloc(sizeof(struct ggml_tallocr));
 

ggml-alloc.h

@@ -52,8 +52,10 @@ typedef struct ggml_tallocr * ggml_tallocr_t;
 
 GGML_API ggml_tallocr_t ggml_tallocr_new(void * data, size_t size, size_t alignment);
 GGML_API ggml_tallocr_t ggml_tallocr_new_measure(size_t alignment);
-GGML_API ggml_tallocr_t ggml_tallocr_new_from_buffer(struct ggml_backend_buffer * buffer);
+GGML_API ggml_tallocr_t ggml_tallocr_new_from_buft(struct ggml_backend_buffer_type * buft, size_t size);
 GGML_API ggml_tallocr_t ggml_tallocr_new_from_backend(struct ggml_backend * backend, size_t size); // allocates an owned buffer
+GGML_API ggml_tallocr_t ggml_tallocr_new_from_buffer(struct ggml_backend_buffer * buffer);
+GGML_API ggml_tallocr_t ggml_tallocr_new_measure_from_buft(struct ggml_backend_buffer_type * buft);
 GGML_API ggml_tallocr_t ggml_tallocr_new_measure_from_backend(struct ggml_backend * backend);
 
 GGML_API struct ggml_backend_buffer * ggml_tallocr_get_buffer(ggml_tallocr_t talloc);

ggml-backend.c

@@ -776,6 +776,7 @@ struct ggml_backend_sched {
 
     int n_backends;
     ggml_backend_t backends[GGML_MAX_BACKENDS];
+    ggml_backend_buffer_type_t bufts[GGML_MAX_BACKENDS];
     ggml_tallocr_t  tallocs[GGML_MAX_BACKENDS];
 
     ggml_gallocr_t galloc;
@@ -1334,7 +1335,7 @@ static void sched_reset(ggml_backend_sched_t sched) {
     sched->is_reset = true;
 }
 
-ggml_backend_sched_t ggml_backend_sched_new(ggml_backend_t * backends, int n_backends, size_t graph_size) {
+ggml_backend_sched_t ggml_backend_sched_new(ggml_backend_t * backends, ggml_backend_buffer_type_t * bufts, int n_backends, size_t graph_size) {
     GGML_ASSERT(n_backends > 0);
     GGML_ASSERT(n_backends <= GGML_MAX_BACKENDS);
 
@@ -1348,13 +1349,14 @@ ggml_backend_sched_t ggml_backend_sched_new(ggml_backend_t * backends, int n_bac
     sched->n_backends = n_backends;
     for (int i = 0; i < n_backends; i++) {
         sched->backends[i] = backends[i];
+        sched->bufts[i] = bufts ? bufts[i] : ggml_backend_get_default_buffer_type(backends[i]);
     }
 
     sched->galloc = ggml_gallocr_new();
 
     // init measure allocs for each backend
     for (int i = 0; i < n_backends; i++) {
-        sched->tallocs[i] = ggml_tallocr_new_measure_from_backend(backends[i]);
+        sched->tallocs[i] = ggml_tallocr_new_measure_from_buft(sched->bufts[i]);
     }
 
     sched_reset(sched);
@@ -1387,7 +1389,7 @@ void ggml_backend_sched_init_measure(ggml_backend_sched_t sched, struct ggml_cgr
     for (int i = 0; i < sched->n_backends; i++) {
         size_t size = ggml_tallocr_max_size(sched->tallocs[i]);
         ggml_tallocr_free(sched->tallocs[i]);
-        sched->tallocs[i] = ggml_tallocr_new_from_backend(sched->backends[i], size);
+        sched->tallocs[i] = ggml_tallocr_new_from_buft(sched->bufts[i], size);
     }
 
     sched_reset(sched);

ggml-backend.h

@@ -149,7 +149,7 @@ extern "C" {
     typedef struct ggml_backend_sched * ggml_backend_sched_t;
 
     // Initialize a backend scheduler
-    GGML_API ggml_backend_sched_t  ggml_backend_sched_new(ggml_backend_t * backends, int n_backends, size_t graph_size);
+    GGML_API ggml_backend_sched_t  ggml_backend_sched_new(ggml_backend_t * backends, ggml_backend_buffer_type_t * bufts, int n_backends, size_t graph_size);
     GGML_API void                  ggml_backend_sched_free(ggml_backend_sched_t sched);
     // Initialize backend buffers from a measure graph
     GGML_API void                  ggml_backend_sched_init_measure(ggml_backend_sched_t sched, struct ggml_cgraph * measure_graph);

llama.cpp

@@ -9368,10 +9368,21 @@ struct llama_context * llama_new_context_with_model(
         }
 
         {
+            // buffer types used for the compute buffer of each backend
+            std::vector<ggml_backend_buffer_type_t> backend_buft;
+            for (auto * backend : ctx->backends) {
+                if (ggml_backend_is_cpu(backend)) {
+                    // use host buffers for the CPU backend compute buffer
+                    backend_buft.push_back(llama_default_buffer_type_cpu(true));
+                } else {
+                    backend_buft.push_back(ggml_backend_get_default_buffer_type(backend));
+                }
+            }
+
             // buffer used to store the computation graph and the tensor meta data
             ctx->buf_compute_meta.resize(ggml_tensor_overhead()*LLAMA_MAX_NODES + ggml_graph_overhead());
 
-            ctx->sched = ggml_backend_sched_new(ctx->backends.data(), ctx->backends.size(), LLAMA_MAX_NODES);
+            ctx->sched = ggml_backend_sched_new(ctx->backends.data(), backend_buft.data(), ctx->backends.size(), LLAMA_MAX_NODES);
             ctx->alloc = ggml_backend_sched_get_tallocr(ctx->sched, ctx->backend_cpu);
 
             // build worst-case graph
@@ -9390,7 +9401,7 @@ struct llama_context * llama_new_context_with_model(
             for (ggml_backend_t backend : ctx->backends) {
                 ggml_backend_buffer_t buf = ggml_backend_sched_get_buffer(ctx->sched, backend);
                 LLAMA_LOG_INFO("%s: %10s compute buffer size = %8.2f MiB\n", __func__,
-                        ggml_backend_name(backend),
+                        ggml_backend_buffer_name(buf),
                         ggml_backend_buffer_get_size(buf) / 1024.0 / 1024.0);
             }
         }