From 29432c4eba79283d93a652165799621144da49f7 Mon Sep 17 00:00:00 2001 From: Mohammed Khajapasha Date: Fri, 4 Sep 2015 20:33:31 +0530 Subject: [PATCH] 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: Mohammed Khajapasha Signed-off-by: Elliot Berman --- init/Kconfig | 10 ++++++++++ kernel/printk/printk.c | 10 ++++++++-- 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index a4fa7858f0d8..4c3551545289 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -608,6 +608,16 @@ 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 diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1888f6a3b694..0b1c9553d48f 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2245,6 +2245,8 @@ void resume_console(void) console_unlock(); } +#ifdef CONFIG_CONSOLE_FLUSH_ON_HOTPLUG + /** * console_cpu_notify - print deferred console messages after CPU hotplug * @cpu: unused @@ -2264,6 +2266,8 @@ static int console_cpu_notify(unsigned int cpu) return 0; } +#endif + /** * console_lock - lock the console system for exclusive use. * @@ -2894,7 +2898,7 @@ 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)) @@ -2916,13 +2920,15 @@ 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);