Sleep AI processing when nobody on their Zlevel

code/controllers/subsystems/ai.dm

@@ -9,14 +9,22 @@ SUBSYSTEM_DEF(ai)
 	var/list/processing = list()
 	var/list/currentrun = list()
 
+	var/slept_mobs = 0
+	var/list/process_z = list()	
+
 /datum/controller/subsystem/ai/stat_entry(msg_prefix)
-	var/list/msg = list(msg_prefix)
-	msg += "P:[processing.len]"
-	..(msg.Join())
+	..("P: [processing.len] | S: [slept_mobs]")
 
 /datum/controller/subsystem/ai/fire(resumed = 0)
 	if (!resumed)
 		src.currentrun = processing.Copy()
+		process_z.Cut()
+		slept_mobs = 0
+		var/level = 1
+		while(process_z.len < GLOB.living_players_by_zlevel.len)
+			process_z.len++
+			process_z[level] = GLOB.living_players_by_zlevel[level].len
+			level++
 
 	//cache for sanic speed (lists are references anyways)
 	var/list/currentrun = src.currentrun
@@ -26,7 +34,12 @@ SUBSYSTEM_DEF(ai)
 		--currentrun.len
 		if(!A || QDELETED(A) || A.busy) // Doesn't exist or won't exist soon or not doing it this tick
 			continue
-		A.handle_strategicals()
+		
+		if(process_z[get_z(A.holder)])
+			A.handle_strategicals()
+		else
+			slept_mobs++
+			A.set_stance(STANCE_IDLE)
 
 		if(MC_TICK_CHECK)
 			return

code/game/world.dm

@@ -648,10 +648,15 @@ proc/establish_old_db_connection()
 /world/proc/max_z_changed()
 	if(!istype(GLOB.players_by_zlevel, /list))
 		GLOB.players_by_zlevel = new /list(world.maxz, 0)
+		GLOB.living_players_by_zlevel = new /list(world.maxz, 0)
+	
 	while(GLOB.players_by_zlevel.len < world.maxz)
 		GLOB.players_by_zlevel.len++
 		GLOB.players_by_zlevel[GLOB.players_by_zlevel.len] = list()
 		
+		GLOB.living_players_by_zlevel.len++
+		GLOB.living_players_by_zlevel[GLOB.living_players_by_zlevel.len] = list()
+
 // Call this to make a new blank z-level, don't modify maxz directly.
 /world/proc/increment_max_z()
 	maxz++

code/modules/ai/ai_holder.dm

@@ -318,9 +318,11 @@
 		if(STANCE_MOVE)
 			if(hostile && find_target()) // This will switch its stance.
 				ai_log("handle_stance_strategical() : STANCE_MOVE, found target and was inturrupted.", AI_LOG_TRACE)
+				return
 		if(STANCE_FOLLOW)
 			if(hostile && find_target()) // This will switch its stance.
 				ai_log("handle_stance_strategical() : STANCE_FOLLOW, found target and was inturrupted.", AI_LOG_TRACE)
+				return
 			else if(leader)
 				ai_log("handle_stance_strategical() : STANCE_FOLLOW, going to calculate_path([leader]).", AI_LOG_TRACE)
 				calculate_path(leader)
@@ -359,5 +361,6 @@
 	if(ai_holder)
 		ai_holder.receive_taunt(taunter, force_target_switch)
 
+#undef AI_NO_PROCESS
 #undef AI_PROCESSING
 #undef AI_FASTPROCESSING

code/modules/ai/ai_holder_disabled.dm

@@ -6,7 +6,7 @@
 // If our holder is able to do anything.
 /datum/ai_holder/proc/can_act()
 	if(!holder) // Holder missing.
-		manage_processing(AI_NO_PROCESS)
+		manage_processing(0)
 		return FALSE
 	if(holder.stat) // Dead or unconscious.
 		ai_log("can_act() : Stat was non-zero ([holder.stat]).", AI_LOG_TRACE)

code/modules/mob/living/simple_mob/simple_mob.dm

@@ -156,6 +156,9 @@
 	// contained in a cage
 	var/in_stasis = 0
 
+	// don't process me if there's nobody around to see it
+	low_priority = TRUE
+
 /mob/living/simple_mob/Initialize()
 	verbs -= /mob/verb/observe
 	health = maxHealth

code/modules/mob/mob.dm

@@ -1200,6 +1200,16 @@ mob/proc/yank_out_object()
 		else
 			registered_z = null
 
+GLOBAL_LIST_EMPTY(living_players_by_zlevel)
+/mob/living/update_client_z(new_z)
+	var/precall_reg_z = registered_z
+	. = ..() // will update registered_z if necessary
+	if(precall_reg_z != registered_z) // parent did work, let's do work too
+		if(precall_reg_z)
+			GLOB.living_players_by_zlevel[precall_reg_z] -= src
+		if(registered_z)
+			GLOB.living_players_by_zlevel[registered_z] += src
+
 /mob/onTransitZ(old_z, new_z)
 	..()
 	update_client_z(new_z)