rpc : do not wait for response when sending RPC_CMD_SET_TENSOR (#12943)

RPC_CMD_SET_TENSOR always returns an empty response and we send this 4
times per token. We can improve TG speed if we don't wait for this empty
response.

The performance impact of this change depends on the network latency.

ggml/include/ggml-rpc.h

@@ -7,7 +7,7 @@
 extern "C" {
 #endif
 
-#define RPC_PROTO_MAJOR_VERSION    1
+#define RPC_PROTO_MAJOR_VERSION    2
 #define RPC_PROTO_MINOR_VERSION    0
 #define RPC_PROTO_PATCH_VERSION    0
 #define GGML_RPC_MAX_SERVERS       16

ggml/src/ggml-rpc/ggml-rpc.cpp

@@ -378,8 +378,8 @@ static bool parse_endpoint(const std::string & endpoint, std::string & host, int
 }
 
 // RPC request : | rpc_cmd (1 byte) | request_size (8 bytes) | request_data (request_size bytes) |
-// RPC response: | response_size (8 bytes) | response_data (response_size bytes) |
-static bool send_rpc_cmd(const std::shared_ptr<socket_t> & sock, enum rpc_cmd cmd, const void * input, size_t input_size, void * output, size_t output_size) {
+// No response
+static bool send_rpc_cmd(const std::shared_ptr<socket_t> & sock, enum rpc_cmd cmd, const void * input, size_t input_size) {
     uint8_t cmd_byte = cmd;
     if (!send_data(sock->fd, &cmd_byte, sizeof(cmd_byte))) {
         return false;
@@ -390,6 +390,15 @@ static bool send_rpc_cmd(const std::shared_ptr<socket_t> & sock, enum rpc_cmd cm
     if (!send_data(sock->fd, input, input_size)) {
         return false;
     }
+    return true;
+}
+
+// RPC request : | rpc_cmd (1 byte) | request_size (8 bytes) | request_data (request_size bytes) |
+// RPC response: | response_size (8 bytes) | response_data (response_size bytes) |
+static bool send_rpc_cmd(const std::shared_ptr<socket_t> & sock, enum rpc_cmd cmd, const void * input, size_t input_size, void * output, size_t output_size) {
+    if (!send_rpc_cmd(sock, cmd, input, input_size)) {
+        return false;
+    }
     // TODO: currently the output_size is always known, do we need support for commands with variable output size?
     // even if we do, we can skip sending output_size from the server for commands with known output size
     uint64_t out_size;
@@ -555,7 +564,7 @@ static void ggml_backend_rpc_buffer_set_tensor(ggml_backend_buffer_t buffer, ggm
     memcpy(input.data(), &rpc_tensor, sizeof(rpc_tensor));
     memcpy(input.data() + sizeof(rpc_tensor), &offset, sizeof(offset));
     memcpy(input.data() + sizeof(rpc_tensor) + sizeof(offset), data, size);
-    bool status = send_rpc_cmd(ctx->sock, RPC_CMD_SET_TENSOR, input.data(), input.size(), nullptr, 0);
+    bool status = send_rpc_cmd(ctx->sock, RPC_CMD_SET_TENSOR, input.data(), input.size());
     GGML_ASSERT(status);
 }
 
@@ -1428,9 +1437,6 @@ static void rpc_serve_client(ggml_backend_t backend, const char * cache_dir,
                 if (!server.set_tensor(input)) {
                     return;
                 }
-                if (!send_msg(sockfd, nullptr, 0)) {
-                    return;
-                }
                 break;
             }
             case RPC_CMD_SET_TENSOR_HASH: {