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Commit fc362b23 authored by Mohammed Khajapasha's avatar Mohammed Khajapasha Committed by Prasad Sodagudi
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printk: Make the console flush configurable in hotplug path 



The thread which initiates the hot plug can get scheduled
out, while trying to acquire the console lock,
thus increasing the hot plug latency. This option
allows to selectively disable the console flush and
in turn reduce the hot plug latency.

Change-Id: I42507804d321b29b7761146a6c175d959bf79925
Signed-off-by: default avatarMohammed Khajapasha <mkhaja@codeaurora.org>
Signed-off-by: default avatarPrasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: default avatarNeeraj Upadhyay <neeraju@codeaurora.org>
parent e14e6b52

init/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -531,6 +531,16 @@ 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

+8 −2
Original line number Diff line number Diff line
@@ -2021,6 +2021,8 @@ void resume_console(void) 
	console_unlock();

}



#ifdef CONFIG_CONSOLE_FLUSH_ON_HOTPLUG



/**

 * console_cpu_notify - print deferred console messages after CPU hotplug

 * @cpu: unused
@@ -2040,6 +2042,8 @@ static int console_cpu_notify(unsigned int cpu) 
	return 0;

}



#endif



/**

 * console_lock - lock the console system for exclusive use.

 *
@@ -2652,7 +2656,7 @@ void __init console_init(void) 
static int __init printk_late_init(void)

{

	struct console *con;

	int ret;

	int ret = 0;



	for_each_console(con) {

		if (!(con->flags & CON_BOOT))
@@ -2674,13 +2678,15 @@ static int __init printk_late_init(void) 
			unregister_console(con);

		}

	}

#ifdef CONFIG_CONSOLE_FLUSH_ON_HOTPLUG

	ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,

					console_cpu_notify);

	WARN_ON(ret < 0);

	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",

					console_cpu_notify, NULL);

	WARN_ON(ret < 0);

	return 0;

#endif

	return ret;

}

late_initcall(printk_late_init);