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 <mkhaja@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
diff --git a/init/Kconfig b/init/Kconfig
index ba93dd3..0f4ccdc 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -519,6 +519,16 @@
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 2478083..8648dc2 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2178,6 +2178,8 @@
console_unlock();
}
+#ifdef CONFIG_CONSOLE_FLUSH_ON_HOTPLUG
+
/**
* console_cpu_notify - print deferred console messages after CPU hotplug
* @cpu: unused
@@ -2197,6 +2199,8 @@
return 0;
}
+#endif
+
/**
* console_lock - lock the console system for exclusive use.
*
@@ -2808,7 +2812,7 @@
static int __init printk_late_init(void)
{
struct console *con;
- int ret;
+ int ret = 0;
for_each_console(con) {
if (!(con->flags & CON_BOOT))
@@ -2830,13 +2834,15 @@
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);