Merge "printk: Make the console flush configurable in hotplug path"

init/Kconfig

@@ -840,6 +840,16 @@ config LOG_BUF_SHIFT
 		     13 =>  8 KB
 		     12 =>  4 KB
 
+config CONSOLE_FLUSH_ON_HOTPLUG
+	bool "Enable console flush configurable in hot plug code path"
+	depends on HOTPLUG_CPU
+	def_bool n
+	help
+	In cpu hot plug path console lock acquire and release causes the
+	console to flush. If console lock is not free hot plug latency
+	increases. So make console flush configurable in hot plug path
+	and default disabled to help in cpu hot plug latencies.
+
 config LOG_CPU_MAX_BUF_SHIFT
 	int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
 	depends on SMP

kernel/printk/printk.c

@@ -2172,6 +2172,8 @@ void resume_console(void)
 	console_unlock();
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_ON_HOTPLUG
+
 /**
  * console_cpu_notify - print deferred console messages after CPU hotplug
  * @self: notifier struct
@@ -2197,6 +2199,8 @@ static int console_cpu_notify(struct notifier_block *self,
 	return NOTIFY_OK;
 }
 
+#endif
+
 /**
  * console_lock - lock the console system for exclusive use.
  *
@@ -2850,7 +2854,9 @@ static int __init printk_late_init(void)
 				unregister_console(con);
 		}
 	}
+#ifdef CONFIG_CONSOLE_FLUSH_ON_HOTPLUG
 	hotcpu_notifier(console_cpu_notify, 0);
+#endif
 	return 0;
 }
 late_initcall(printk_late_init);