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Commit cf7df378 authored by Robin Holt's avatar Robin Holt Committed by Linus Torvalds
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reboot: rigrate shutdown/reboot to boot cpu 



We recently noticed that reboot of a 1024 cpu machine takes approx 16
minutes of just stopping the cpus.  The slowdown was tracked to commit
f96972f2 ("kernel/sys.c: call disable_nonboot_cpus() in
kernel_restart()").

The current implementation does all the work of hot removing the cpus
before halting the system.  We are switching to just migrating to the
boot cpu and then continuing with shutdown/reboot.

This also has the effect of not breaking x86's command line parameter
for specifying the reboot cpu.  Note, this code was shamelessly copied
from arch/x86/kernel/reboot.c with bits removed pertaining to the
reboot_cpu command line parameter.

Signed-off-by: default avatarRobin Holt <holt@sgi.com>
Tested-by: default avatarShawn Guo <shawn.guo@linaro.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Russ Anderson <rja@sgi.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 16e53dbf

kernel/sys.c

+26 −3
Original line number Diff line number Diff line
@@ -362,6 +362,29 @@ int unregister_reboot_notifier(struct notifier_block *nb) 
}

EXPORT_SYMBOL(unregister_reboot_notifier);



/* Add backwards compatibility for stable trees. */

#ifndef PF_NO_SETAFFINITY

#define PF_NO_SETAFFINITY		PF_THREAD_BOUND

#endif



static void migrate_to_reboot_cpu(void)

{

	/* The boot cpu is always logical cpu 0 */

	int cpu = 0;



	cpu_hotplug_disable();



	/* Make certain the cpu I'm about to reboot on is online */

	if (!cpu_online(cpu))

		cpu = cpumask_first(cpu_online_mask);



	/* Prevent races with other tasks migrating this task */

	current->flags |= PF_NO_SETAFFINITY;



	/* Make certain I only run on the appropriate processor */

	set_cpus_allowed_ptr(current, cpumask_of(cpu));

}



/**

 *	kernel_restart - reboot the system

 *	@cmd: pointer to buffer containing command to execute for restart
@@ -373,7 +396,7 @@ EXPORT_SYMBOL(unregister_reboot_notifier); 
void kernel_restart(char *cmd)

{

	kernel_restart_prepare(cmd);

	disable_nonboot_cpus();

	migrate_to_reboot_cpu();

	syscore_shutdown();

	if (!cmd)

		printk(KERN_EMERG "Restarting system.\n");
@@ -400,7 +423,7 @@ static void kernel_shutdown_prepare(enum system_states state) 
void kernel_halt(void)

{

	kernel_shutdown_prepare(SYSTEM_HALT);

	disable_nonboot_cpus();

	migrate_to_reboot_cpu();

	syscore_shutdown();

	printk(KERN_EMERG "System halted.\n");

	kmsg_dump(KMSG_DUMP_HALT);
@@ -419,7 +442,7 @@ void kernel_power_off(void) 
	kernel_shutdown_prepare(SYSTEM_POWER_OFF);

	if (pm_power_off_prepare)

		pm_power_off_prepare();

	disable_nonboot_cpus();

	migrate_to_reboot_cpu();

	syscore_shutdown();

	printk(KERN_EMERG "Power down.\n");

	kmsg_dump(KMSG_DUMP_POWEROFF);