diff --git a/client/client_state.cpp b/client/client_state.cpp
index 88bf779355f..39c1e1e3afb 100644
--- a/client/client_state.cpp
+++ b/client/client_state.cpp
@@ -1019,18 +1019,30 @@ bool CLIENT_STATE::poll_slow_events() {
     }
 #endif
 
-    bool old_user_active = user_active;
+    // there are 2 reasons to get idle state:
+    // if needed for computing prefs,
+    // or (on Mac) we were started by screensaver
+    //
+    bool get_idle_state = global_prefs.need_idle_state;
+#ifdef __APPLE__
+    if (started_by_screensaver) get_idle_state = true;
+#endif
+    long idle_time;
+    if (get_idle_state) {
+        bool old_user_active = user_active;
 #ifdef ANDROID
-    user_active = device_status.user_active;
+        user_active = device_status.user_active;
 #else
-    long idle_time = host_info.user_idle_time(check_all_logins);
-    user_active = idle_time < global_prefs.idle_time_to_run * 60;
+        idle_time = host_info.user_idle_time(check_all_logins);
+        user_active = idle_time < global_prefs.idle_time_to_run * 60;
 #endif
-
-    if (user_active != old_user_active) {
-        set_n_usable_cpus();
-            // if niu_max_ncpus_pct pref is set, # usable CPUs may change
-        request_schedule_cpus(user_active?"Not idle":"Idle");
+        if (user_active != old_user_active) {
+            set_n_usable_cpus();
+                // if niu_max_ncpus_pct pref is set, # usable CPUs may change
+            request_schedule_cpus(user_active?"Not idle":"Idle");
+        }
+    } else {
+        user_active = false;    // shouldn't matter what it is
     }
 
 #if 0
diff --git a/client/cs_prefs.cpp b/client/cs_prefs.cpp
index 48e8cf0a77d..377a49828df 100644
--- a/client/cs_prefs.cpp
+++ b/client/cs_prefs.cpp
@@ -675,6 +675,9 @@ void CLIENT_STATE::read_global_prefs(
     file_xfers->set_bandwidth_limits(true);
     file_xfers->set_bandwidth_limits(false);
 #endif
+
+    bool have_gpu = coprocs.n_rsc > 1;
+    global_prefs.need_idle_state = global_prefs.get_need_idle_state(have_gpu);
     print_global_prefs();
     request_schedule_cpus("Prefs update");
     request_work_fetch("Prefs update");
@@ -815,6 +818,11 @@ void CLIENT_STATE::print_global_prefs() {
         allowed_disk_usage(total_disk_usage)/GIGA
     );
 #endif
+    if (!global_prefs.need_idle_state) {
+        msg_printf(NULL, MSG_INFO,
+            "-  Preferences don't depend on whether computer is in use"
+        );
+    }
     msg_printf(NULL, MSG_INFO,
         "-  (to change preferences, visit a project web site or select 'Options / Computing preferences...' in the Manager)"
     );
diff --git a/lib/prefs.h b/lib/prefs.h
index 6dca2f5bfe2..5248694d42b 100644
--- a/lib/prefs.h
+++ b/lib/prefs.h
@@ -197,6 +197,8 @@ struct GLOBAL_PREFS {
     bool host_specific;
         // an account manager can set this; if set, don't propagate
     bool override_file_present;
+    bool need_idle_state;
+        // whether idle state makes any difference
 
     GLOBAL_PREFS();
     void defaults();
@@ -214,6 +216,17 @@ struct GLOBAL_PREFS {
         return cpu_scheduling_period_minutes*60;
     }
     static double parse_mod_time(const char*);
+    bool get_need_idle_state(bool have_gpu) {
+        // is any pref set that causes different behavior if user is active?
+        //
+        if (!run_if_user_active) return true;
+        if (have_gpu && !run_gpu_if_user_active) return true;
+        if (suspend_if_no_recent_input) return true;
+        if (niu_cpu_usage_limit && niu_cpu_usage_limit != cpu_usage_limit) return true;
+        if (niu_max_ncpus_pct && niu_max_ncpus_pct != max_ncpus_pct) return true;
+        if (niu_suspend_cpu_usage && niu_suspend_cpu_usage != suspend_cpu_usage) return true;
+        return false;
+    }
 };
 
 #endif