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Commit e4b8535d authored by Srivatsa Vaddagiri's avatar Srivatsa Vaddagiri Committed by Pavankumar Kondeti
Browse files

timer: Queue timers on least power cpu 



There is potential power benefit by offloading timer activity to cpus
of lesser power cost (power cluster). Both high-res and low-res timers
that are not pinned to one cpu are now enqueued on an online CPU
found in least shallow C-state in power-cluster. Prefer the current
CPU in case of a tie.

Change-Id: I2cea26c76972b566dfbfed084e377811a8784172
Signed-off-by: default avatarSrivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent ee630a97

Documentation/scheduler/sched-hmp.txt

+11 −0
Original line number Diff line number Diff line
@@ -1485,6 +1485,17 @@ overcommitted scenario. See notes on sched_spill_nr_run and sched_spill_load for 
how overcommitment threshold is defined and also notes on

'sched_upmigrate_min_nice' tunable.



** 7.26 power_aware_timer_migration



Appears at: /proc/sys/kernel/power_aware_timer_migration



Default value: 0



This tunable helps save power by offloading timer activity to cpus of lesser

power cost (power cluster). Both high-res and low-res timers that are not pinned

to one cpu are now enqueued on an online CPU found in least shallow C-state in

the power-cluster. The current CPU is preferred in case of a tie.



=========================

8. HMP SCHEDULER TRACE POINTS

=========================

include/linux/sched/sysctl.h

+1 −0
Original line number Diff line number Diff line
@@ -67,6 +67,7 @@ extern unsigned int sysctl_sched_downmigrate_pct; 
extern int sysctl_sched_upmigrate_min_nice;

extern unsigned int sysctl_sched_powerband_limit_pct;

extern unsigned int sysctl_sched_boost;

extern unsigned int sysctl_power_aware_timer_migration;



#ifdef CONFIG_SCHED_QHMP

extern unsigned int sysctl_sched_min_runtime;

kernel/sched/core.c

+69 −2
Original line number Diff line number Diff line
@@ -648,6 +648,64 @@ void resched_cpu(int cpu) 


#ifdef CONFIG_SMP

#ifdef CONFIG_NO_HZ_COMMON



#ifdef CONFIG_SCHED_HMP



__read_mostly unsigned int sysctl_power_aware_timer_migration;



/*

 * Return the CPU found in shallowest C-state in least power-cost

 * cluster. Prefer the current CPU when there is a tie.

 */

static int _get_nohz_timer_target_hmp(void)

{

	int i, best_cpu = smp_processor_id();

	int min_cost = INT_MAX, min_cstate = INT_MAX;



	if (!sysctl_power_aware_timer_migration)

		return nr_cpu_ids;



	rcu_read_lock();



	for_each_online_cpu(i) {

		struct rq *rq = cpu_rq(i);

		int cpu_cost = power_cost(i, 0);

		int cstate = rq->cstate;



		if (power_delta_exceeded(cpu_cost, min_cost)) {

			if (cpu_cost > min_cost)

				continue;



			best_cpu = i;

			min_cost = cpu_cost;

			min_cstate = cstate;

			continue;

		}



		if (cstate < min_cstate || (i == smp_processor_id() &&

					cstate == min_cstate)) {

			best_cpu = i;

			min_cstate = cstate;

		}

	}

	rcu_read_unlock();



	return best_cpu;

}



#else



static int _get_nohz_timer_target_hmp(void)

{

	/*

	 * sched_enable_hmp = 0 for !CONFIG_SCHED_HMP, which means we should not

	 * come here for !CONFIG_SCHED_HMP

	 */

	return raw_smp_processor_id();

}



#endif



/*

 * In the semi idle case, use the nearest busy cpu for migrating timers

 * from an idle cpu.  This is good for power-savings.
@@ -659,10 +717,19 @@ void resched_cpu(int cpu) 
int get_nohz_timer_target(int pinned)

{

	int cpu = smp_processor_id();

	int i;

	int i, lower_power_cpu;

	struct sched_domain *sd;



	if (pinned || !get_sysctl_timer_migration() || !idle_cpu(cpu))

	if (pinned || !get_sysctl_timer_migration())

		return cpu;



	if (sched_enable_hmp) {

		lower_power_cpu =  _get_nohz_timer_target_hmp();

		if (lower_power_cpu < nr_cpu_ids)

			return lower_power_cpu;

	}



	if (!idle_cpu(cpu))

		return cpu;



	rcu_read_lock();

kernel/sched/qhmp_core.c

+69 −2
Original line number Diff line number Diff line
@@ -648,6 +648,64 @@ void resched_cpu(int cpu) 


#ifdef CONFIG_SMP

#ifdef CONFIG_NO_HZ_COMMON



#ifdef CONFIG_SCHED_HMP



__read_mostly unsigned int sysctl_power_aware_timer_migration;



/*

 * Return the CPU found in shallowest C-state in least power-cost

 * cluster. Prefer the current CPU when there is a tie.

 */

static int _get_nohz_timer_target_hmp(void)

{

	int i, best_cpu = smp_processor_id();

	int min_cost = INT_MAX, min_cstate = INT_MAX;



	if (!sysctl_power_aware_timer_migration)

		return nr_cpu_ids;



	rcu_read_lock();



	for_each_online_cpu(i) {

		struct rq *rq = cpu_rq(i);

		int cpu_cost = power_cost(0, i);

		int cstate = rq->cstate;



		if (power_delta_exceeded(cpu_cost, min_cost)) {

			if (cpu_cost > min_cost)

				continue;



			best_cpu = i;

			min_cost = cpu_cost;

			min_cstate = cstate;

			continue;

		}



		if (cstate < min_cstate || (i == smp_processor_id() &&

					cstate == min_cstate)) {

			best_cpu = i;

			min_cstate = cstate;

		}

	}

	rcu_read_unlock();



	return best_cpu;

}



#else



static int _get_nohz_timer_target_hmp(void)

{

	/*

	 * sched_enable_hmp = 0 for !CONFIG_SCHED_HMP, which means we should not

	 * come here for !CONFIG_SCHED_HMP

	 */

	return raw_smp_processor_id();

}



#endif



/*

 * In the semi idle case, use the nearest busy cpu for migrating timers

 * from an idle cpu.  This is good for power-savings.
@@ -659,10 +717,19 @@ void resched_cpu(int cpu) 
int get_nohz_timer_target(int pinned)

{

	int cpu = smp_processor_id();

	int i;

	int i, lower_power_cpu;

	struct sched_domain *sd;



	if (pinned || !get_sysctl_timer_migration() || !idle_cpu(cpu))

	if (pinned || !get_sysctl_timer_migration())

		return cpu;



	if (sched_enable_hmp) {

		lower_power_cpu =  _get_nohz_timer_target_hmp();

		if (lower_power_cpu < nr_cpu_ids)

			return lower_power_cpu;

	}



	if (!idle_cpu(cpu))

		return cpu;



	rcu_read_lock();

kernel/sched/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -934,6 +934,7 @@ extern void sched_account_irqtime(int cpu, struct task_struct *curr, 
unsigned int cpu_temp(int cpu);

extern unsigned int nr_eligible_big_tasks(int cpu);

extern void update_up_down_migrate(void);

extern int power_delta_exceeded(unsigned int cpu_cost, unsigned int base_cost);



/*

 * 'load' is in reference to "best cpu" at its best frequency.