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Commit fd40937a authored by Vikram Mulukutla's avatar Vikram Mulukutla
Browse files

idle: Implement a per-cpu idle-polling mode 



cpu_idle_poll_ctrl provides a way of switching the
idle thread to use cpu_idle_poll instead of the arch
specific lower power mode callbacks (arch_cpu_idle).
cpu_idle_poll spins on a flag in a tight loop with
interrupts enabled.

In some cases it may be useful to enter the tight loop
polling mode only on a particular CPU. This allows
other CPUs to continue using the arch specific low
power mode callbacks. Provide an API that allows this.

Change-Id: I7c47c3590eb63345996a1c780faa79dbd1d9fdb4
Signed-off-by: default avatarVikram Mulukutla <markivx@codeaurora.org>
parent 1142bb4b

include/linux/cpu.h

+1 −0
Original line number Diff line number Diff line
@@ -288,6 +288,7 @@ void cpu_startup_entry(enum cpuhp_state state); 
void cpu_idle(void);



void cpu_idle_poll_ctrl(bool enable);

void per_cpu_idle_poll_ctrl(int cpu, bool enable);



void arch_cpu_idle(void);

void arch_cpu_idle_prepare(void);

kernel/cpu/idle.c

+25 −2
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
#include <linux/tick.h>

#include <linux/mm.h>

#include <linux/stackprotector.h>

#include <linux/percpu.h>



#include <asm/tlb.h>
@@ -26,6 +27,24 @@ void cpu_idle_poll_ctrl(bool enable) 
	mb();

}



static DEFINE_PER_CPU(int, idle_force_poll);



void per_cpu_idle_poll_ctrl(int cpu, bool enable)

{

	if (enable) {

		per_cpu(idle_force_poll, cpu)++;

	} else {

		per_cpu(idle_force_poll, cpu)--;

		WARN_ON_ONCE(per_cpu(idle_force_poll, cpu) < 0);

	}



	/*

	 * Make sure poll mode is entered on the relevant CPU after the flag is

	 * set

	 */

	mb();

}



#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP

static int __init cpu_idle_poll_setup(char *__unused)

{
@@ -47,7 +66,8 @@ static inline int cpu_idle_poll(void) 
	rcu_idle_enter();

	trace_cpu_idle_rcuidle(0, smp_processor_id());

	local_irq_enable();

	while (!tif_need_resched() && cpu_idle_force_poll)

	while (!tif_need_resched() && (cpu_idle_force_poll ||

		__get_cpu_var(idle_force_poll)))

		cpu_relax();

	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());

	rcu_idle_exit();
@@ -89,7 +109,9 @@ static void cpu_idle_loop(void) 
			 * know that the IPI is going to arrive right

			 * away

			 */

			if (cpu_idle_force_poll || tick_check_broadcast_expired()) {

			if (cpu_idle_force_poll ||

			    tick_check_broadcast_expired() ||

			    __get_cpu_var(idle_force_poll)) {

				cpu_idle_poll();

			} else {

				if (!current_clr_polling_and_test()) {
@@ -133,5 +155,6 @@ void cpu_startup_entry(enum cpuhp_state state) 
#endif

	__current_set_polling();

	arch_cpu_idle_prepare();

	per_cpu(idle_force_poll, smp_processor_id()) = 0;

	cpu_idle_loop();

}