metal : reduce rset heartbeat from 500ms -> 5ms (ggml-org#24074)

(cherry picked from commit 3d19986)

Author: ggerganov

ggml/src/ggml-metal/ggml-metal-device.m

@@ -547,6 +547,8 @@ void ggml_metal_encoder_end_encoding(ggml_metal_encoder_t encoder) {
     // number of seconds since the last graph computation
     // keep the residency sets wired for that amount of time to avoid being collected by the OS
     int keep_alive_s;
+    int loops_per_s;
+    int time_per_loop_ms;
 
     // background heartbeat thread to keep the residency sets alive
     atomic_bool d_stop;
@@ -573,10 +575,13 @@ ggml_metal_rsets_t ggml_metal_rsets_init(void) {
         res->keep_alive_s = 3*60;
     }
 
+    res->time_per_loop_ms = 5;
+    res->loops_per_s = 1000/res->time_per_loop_ms;
+
     GGML_LOG_INFO("%s: creating a residency set collection (keep_alive = %d s)\n", __func__, res->keep_alive_s);
 
     atomic_store_explicit(&res->d_stop, false, memory_order_relaxed);
-    atomic_store_explicit(&res->d_loop, 2*res->keep_alive_s, memory_order_relaxed);
+    atomic_store_explicit(&res->d_loop, res->loops_per_s*res->keep_alive_s, memory_order_relaxed);
 
     res->d_group = dispatch_group_create();
 
@@ -599,8 +604,7 @@ ggml_metal_rsets_t ggml_metal_rsets_init(void) {
                       [res->lock unlock];
                   }
 
-                  // half a second
-                  usleep(500 * 1000);
+                  usleep(res->time_per_loop_ms * 1000);
               }
         }
 #endif
@@ -979,7 +983,7 @@ void ggml_metal_device_rsets_keep_alive(ggml_metal_device_t dev) {
         return;
     }
 
-    atomic_store_explicit(&dev->rsets->d_loop, 2*dev->rsets->keep_alive_s, memory_order_relaxed);
+    atomic_store_explicit(&dev->rsets->d_loop, dev->rsets->loops_per_s*dev->rsets->keep_alive_s, memory_order_relaxed);
 }
 
 struct ggml_metal_event {