metal : show all Metal device instances in the system (#2952)

* ggml_metal_init: Show all Metal device instances in the system

Also show the default Metal device that was picked.

* Update ggml-metal.m

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

ggml-metal.m

@@ -116,10 +116,24 @@ static NSString * const msl_library_source = @"see metal.metal";
 struct ggml_metal_context * ggml_metal_init(int n_cb) {
     metal_printf("%s: allocating\n", __func__);
 
-    struct ggml_metal_context * ctx = malloc(sizeof(struct ggml_metal_context));
+    // Show all the Metal device instances in the system
+    NSArray * devices = MTLCopyAllDevices();
+    id <MTLDevice> device;
+    NSString * s;
+    for (device in devices) {
+        s = [device name];
+        metal_printf("%s: found device: %s\n", __func__, [s UTF8String]);
+    }
 
+    // Pick and show default Metal device
+    device = MTLCreateSystemDefaultDevice();
+    s = [device name];
+    metal_printf("%s: picking default device: %s\n", __func__, [s UTF8String]);
+
+    // Configure context
+    struct ggml_metal_context * ctx = malloc(sizeof(struct ggml_metal_context));
+    ctx->device = device;
     ctx->n_cb   = MIN(n_cb, GGML_METAL_MAX_BUFFERS);
-    ctx->device = MTLCreateSystemDefaultDevice();
     ctx->queue  = [ctx->device newCommandQueue];
     ctx->n_buffers = 0;
     ctx->concur_list_len = 0;