Commit 7d5f9c0f authored by Zwane Mwaikambo's avatar Zwane Mwaikambo Committed by Tony Luck
Browse files

[IA64] reduce cacheline bouncing in cpu_idle_wait 



Andi noted that during normal runtime cpu_idle_map is bounced around a lot,
and occassionally at a higher frequency than the timer interrupt wakeup
which we normally exit pm_idle from.  So switch to a percpu variable.

I didn't move things to the slow path because it would involve adding
scheduler code to wakeup the idle thread on the cpus we're waiting for.

Signed-off-by: default avatarZwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent de7548d0

arch/ia64/kernel/process.c

+26 −15
Original line number Diff line number Diff line
@@ -50,7 +50,7 @@ 
#include "sigframe.h"



void (*ia64_mark_idle)(int);

static cpumask_t cpu_idle_map;

static DEFINE_PER_CPU(unsigned int, cpu_idle_state);



unsigned long boot_option_idle_override = 0;

EXPORT_SYMBOL(boot_option_idle_override);
@@ -223,19 +223,30 @@ static inline void play_dead(void) 
}

#endif /* CONFIG_HOTPLUG_CPU */





void cpu_idle_wait(void)

{

        int cpu;

	unsigned int cpu, this_cpu = get_cpu();

	cpumask_t map;



        for_each_online_cpu(cpu)

                cpu_set(cpu, cpu_idle_map);

	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);

                cpus_and(map, cpu_idle_map, cpu_online_map);

		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);

	} while (!cpus_empty(map));

}

EXPORT_SYMBOL_GPL(cpu_idle_wait);
@@ -244,7 +255,6 @@ void __attribute__((noreturn)) 
cpu_idle (void)

{

	void (*mark_idle)(int) = ia64_mark_idle;

	int cpu = smp_processor_id();



	/* endless idle loop with no priority at all */

	while (1) {
@@ -255,12 +265,13 @@ cpu_idle (void) 
		while (!need_resched()) {

			void (*idle)(void);



			if (__get_cpu_var(cpu_idle_state))

				__get_cpu_var(cpu_idle_state) = 0;



			rmb();

			if (mark_idle)

				(*mark_idle)(1);



			if (cpu_isset(cpu, cpu_idle_map))

				cpu_clear(cpu, cpu_idle_map);

			rmb();

			idle = pm_idle;

			if (!idle)

				idle = default_idle;

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