rpc : add support for multiple devices (ggml-org#16276)

* rpc : add support for multiple devices

Allow rpc-server to expose multiple devices from a single endpoint.
Change RPC protocol to include device identifier where needed.

closes: ggml-org#15210

* fixes

* use ggml_backend_reg_t

* address review comments

* fix llama-bench backend report

* address review comments, change device naming

* fix cmd order

Author: rgerganov

common/arg.cpp

@@ -1615,18 +1615,14 @@ static void add_rpc_devices(const std::string & servers) {
     if (!rpc_reg) {
         throw std::invalid_argument("failed to find RPC backend");
     }
-    typedef ggml_backend_dev_t (*ggml_backend_rpc_add_device_t)(const char * endpoint);
-    ggml_backend_rpc_add_device_t ggml_backend_rpc_add_device_fn = (ggml_backend_rpc_add_device_t) ggml_backend_reg_get_proc_address(rpc_reg, "ggml_backend_rpc_add_device");
-    if (!ggml_backend_rpc_add_device_fn) {
-        throw std::invalid_argument("failed to find RPC device add function");
+    typedef ggml_backend_reg_t (*ggml_backend_rpc_add_server_t)(const char * endpoint);
+    ggml_backend_rpc_add_server_t ggml_backend_rpc_add_server_fn = (ggml_backend_rpc_add_server_t) ggml_backend_reg_get_proc_address(rpc_reg, "ggml_backend_rpc_add_server");
+    if (!ggml_backend_rpc_add_server_fn) {
+        throw std::invalid_argument("failed to find RPC add server function");
     }
     for (const auto & server : rpc_servers) {
-        ggml_backend_dev_t dev = ggml_backend_rpc_add_device_fn(server.c_str());
-        if (dev) {
-            ggml_backend_device_register(dev);
-        } else {
-            throw std::invalid_argument("failed to register RPC device");
-        }
+        auto reg = ggml_backend_rpc_add_server_fn(server.c_str());
+        ggml_backend_register(reg);
     }
 }
 

ggml/include/ggml-backend.h

@@ -215,6 +215,8 @@ extern "C" {
     // Backend registry
     //
 
+    GGML_API void ggml_backend_register(ggml_backend_reg_t reg);
+
     GGML_API void ggml_backend_device_register(ggml_backend_dev_t device);
 
     // Backend (reg) enumeration

ggml/include/ggml-rpc.h

@@ -7,26 +7,25 @@
 extern "C" {
 #endif
 
-#define RPC_PROTO_MAJOR_VERSION    2
+#define RPC_PROTO_MAJOR_VERSION    3
 #define RPC_PROTO_MINOR_VERSION    0
 #define RPC_PROTO_PATCH_VERSION    0
 #define GGML_RPC_MAX_SERVERS       16
 
 // backend API
-GGML_BACKEND_API ggml_backend_t ggml_backend_rpc_init(const char * endpoint);
+GGML_BACKEND_API ggml_backend_t ggml_backend_rpc_init(const char * endpoint, uint32_t device);
 GGML_BACKEND_API bool ggml_backend_is_rpc(ggml_backend_t backend);
 
-GGML_BACKEND_API ggml_backend_buffer_type_t ggml_backend_rpc_buffer_type(const char * endpoint);
+GGML_BACKEND_API ggml_backend_buffer_type_t ggml_backend_rpc_buffer_type(const char * endpoint, uint32_t device);
 
-GGML_BACKEND_API void ggml_backend_rpc_get_device_memory(const char * endpoint, size_t * free, size_t * total);
+GGML_BACKEND_API void ggml_backend_rpc_get_device_memory(const char * endpoint, uint32_t device, size_t * free, size_t * total);
 
-GGML_BACKEND_API void ggml_backend_rpc_start_server(ggml_backend_t backend, const char * endpoint,
-                                                    const char * cache_dir,
-                                                    size_t free_mem, size_t total_mem);
+GGML_BACKEND_API void ggml_backend_rpc_start_server(const char * endpoint, const char * cache_dir,
+                                                    size_t n_threads, size_t n_devices,
+                                                    ggml_backend_dev_t * devices, size_t * free_mem, size_t * total_mem);
 
 GGML_BACKEND_API ggml_backend_reg_t ggml_backend_rpc_reg(void);
-
-GGML_BACKEND_API ggml_backend_dev_t ggml_backend_rpc_add_device(const char * endpoint);
+GGML_BACKEND_API ggml_backend_reg_t ggml_backend_rpc_add_server(const char * endpoint);
 
 #ifdef  __cplusplus
 }

ggml/src/ggml-backend-impl.h

@@ -209,9 +209,6 @@ extern "C" {
         void * context;
     };
 
-    // Internal backend registry API
-    GGML_API void ggml_backend_register(ggml_backend_reg_t reg);
-
     // Add backend dynamic loading support to the backend
 
     // Initialize the backend