Commit 783e391b authored by Venki Pallipadi's avatar Venki Pallipadi Committed by Linus Torvalds
Browse files

x86: Simplify cpu_idle_wait 

This patch also resolves hangs on boot:
	http://lkml.org/lkml/2008/2/23/263
	http://bugzilla.kernel.org/show_bug.cgi?id=10093



The bug was causing once-in-few-reboots 10-15 sec wait during boot on
certain laptops.

Earlier commit 40d6a146 added
smp_call_function in cpu_idle_wait() to kick cpus that are in tickless
idle.  Looking at cpu_idle_wait code at that time, code seemed to be
over-engineered for a case which is rarely used (while changing idle
handler).

Below is a simplified version of cpu_idle_wait, which just makes a dummy
smp_call_function to all cpus, to make them come out of old idle handler
and start using the new idle handler.  It eliminates code in the idle
loop to handle cpu_idle_wait.

Signed-off-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a1e58bbd

arch/x86/kernel/process_32.c

+11 −36
Original line number Diff line number Diff line
@@ -82,7 +82,6 @@ unsigned long thread_saved_pc(struct task_struct *tsk) 
 */

void (*pm_idle)(void);

EXPORT_SYMBOL(pm_idle);

static DEFINE_PER_CPU(unsigned int, cpu_idle_state);



void disable_hlt(void)

{
@@ -190,9 +189,6 @@ void cpu_idle(void) 
		while (!need_resched()) {

			void (*idle)(void);



			if (__get_cpu_var(cpu_idle_state))

				__get_cpu_var(cpu_idle_state) = 0;



			check_pgt_cache();

			rmb();

			idle = pm_idle;
@@ -220,40 +216,19 @@ static void do_nothing(void *unused) 
{

}



void cpu_idle_wait(void)

{

	unsigned int cpu, this_cpu = get_cpu();

	cpumask_t map, tmp = current->cpus_allowed;



	set_cpus_allowed(current, cpumask_of_cpu(this_cpu));

	put_cpu();



	cpus_clear(map);

	for_each_online_cpu(cpu) {

		per_cpu(cpu_idle_state, cpu) = 1;

		cpu_set(cpu, map);

	}



	__get_cpu_var(cpu_idle_state) = 0;



	wmb();

	do {

		ssleep(1);

		for_each_online_cpu(cpu) {

			if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))

				cpu_clear(cpu, map);

		}

		cpus_and(map, map, cpu_online_map);

/*

		 * We waited 1 sec, if a CPU still did not call idle

		 * it may be because it is in idle and not waking up

		 * because it has nothing to do.

		 * Give all the remaining CPUS a kick.

 * cpu_idle_wait - Used to ensure that all the CPUs discard old value of

 * pm_idle and update to new pm_idle value. Required while changing pm_idle

 * handler on SMP systems.

 *

 * Caller must have changed pm_idle to the new value before the call. Old

 * pm_idle value will not be used by any CPU after the return of this function.

 */

		smp_call_function_mask(map, do_nothing, NULL, 0);

	} while (!cpus_empty(map));



	set_cpus_allowed(current, tmp);

void cpu_idle_wait(void)

{

	smp_mb();

	/* kick all the CPUs so that they exit out of pm_idle */

	smp_call_function(do_nothing, NULL, 0, 1);

}

EXPORT_SYMBOL_GPL(cpu_idle_wait);

arch/x86/kernel/process_64.c

+11 −36
Original line number Diff line number Diff line
@@ -63,7 +63,6 @@ EXPORT_SYMBOL(boot_option_idle_override); 
 */

void (*pm_idle)(void);

EXPORT_SYMBOL(pm_idle);

static DEFINE_PER_CPU(unsigned int, cpu_idle_state);



static ATOMIC_NOTIFIER_HEAD(idle_notifier);
@@ -173,9 +172,6 @@ void cpu_idle(void) 
		while (!need_resched()) {

			void (*idle)(void);



			if (__get_cpu_var(cpu_idle_state))

				__get_cpu_var(cpu_idle_state) = 0;



			rmb();

			idle = pm_idle;

			if (!idle)
@@ -207,40 +203,19 @@ static void do_nothing(void *unused) 
{

}



void cpu_idle_wait(void)

{

	unsigned int cpu, this_cpu = get_cpu();

	cpumask_t map, tmp = current->cpus_allowed;



	set_cpus_allowed(current, cpumask_of_cpu(this_cpu));

	put_cpu();



	cpus_clear(map);

	for_each_online_cpu(cpu) {

		per_cpu(cpu_idle_state, cpu) = 1;

		cpu_set(cpu, map);

	}



	__get_cpu_var(cpu_idle_state) = 0;



	wmb();

	do {

		ssleep(1);

		for_each_online_cpu(cpu) {

			if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))

				cpu_clear(cpu, map);

		}

		cpus_and(map, map, cpu_online_map);

/*

		 * We waited 1 sec, if a CPU still did not call idle

		 * it may be because it is in idle and not waking up

		 * because it has nothing to do.

		 * Give all the remaining CPUS a kick.

 * cpu_idle_wait - Used to ensure that all the CPUs discard old value of

 * pm_idle and update to new pm_idle value. Required while changing pm_idle

 * handler on SMP systems.

 *

 * Caller must have changed pm_idle to the new value before the call. Old

 * pm_idle value will not be used by any CPU after the return of this function.

 */

		smp_call_function_mask(map, do_nothing, 0, 0);

	} while (!cpus_empty(map));



	set_cpus_allowed(current, tmp);

void cpu_idle_wait(void)

{

	smp_mb();

	/* kick all the CPUs so that they exit out of pm_idle */

	smp_call_function(do_nothing, NULL, 0, 1);

}

EXPORT_SYMBOL_GPL(cpu_idle_wait);

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