Commit 46e49b38 authored by Venkatesh Pallipadi's avatar Venkatesh Pallipadi Committed by Ingo Molnar
Browse files

sched: Wholesale removal of sd_idle logic 

sd_idle logic was introduced way back in 2005 (commit 5969fe06),
as an HT optimization.

As per the discussion in the thread here:

  lkml - sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1
  https://patchwork.kernel.org/patch/532501/



The capacity based logic in the load balancer right now handles this
in a much cleaner way, handling more than 2 SMT siblings etc, and sd_idle
does not seem to bring any additional benefits. sd_idle logic also has
some bugs that has performance impact. Here is the patch that removes
the sd_idle logic altogether.

Also, there was a dependency of sched_mc_power_savings == 2, with sd_idle
logic.

Signed-off-by: default avatarVenkatesh Pallipadi <venki@google.com>
Acked-by: default avatarVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1297723130-693-1-git-send-email-venki@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 48fa4b8e

kernel/sched_fair.c

+11 −42
Original line number Diff line number Diff line
@@ -2672,7 +2672,6 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group) 
 * @this_cpu: Cpu for which load balance is currently performed.

 * @idle: Idle status of this_cpu

 * @load_idx: Load index of sched_domain of this_cpu for load calc.

 * @sd_idle: Idle status of the sched_domain containing group.

 * @local_group: Does group contain this_cpu.

 * @cpus: Set of cpus considered for load balancing.

 * @balance: Should we balance.
@@ -2680,7 +2679,7 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group) 
 */

static inline void update_sg_lb_stats(struct sched_domain *sd,

			struct sched_group *group, int this_cpu,

			enum cpu_idle_type idle, int load_idx, int *sd_idle,

			enum cpu_idle_type idle, int load_idx,

			int local_group, const struct cpumask *cpus,

			int *balance, struct sg_lb_stats *sgs)

{
@@ -2700,9 +2699,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd, 
	for_each_cpu_and(i, sched_group_cpus(group), cpus) {

		struct rq *rq = cpu_rq(i);



		if (*sd_idle && rq->nr_running)

			*sd_idle = 0;



		/* Bias balancing toward cpus of our domain */

		if (local_group) {

			if (idle_cpu(i) && !first_idle_cpu) {
@@ -2817,15 +2813,13 @@ static bool update_sd_pick_busiest(struct sched_domain *sd, 
 * @sd: sched_domain whose statistics are to be updated.

 * @this_cpu: Cpu for which load balance is currently performed.

 * @idle: Idle status of this_cpu

 * @sd_idle: Idle status of the sched_domain containing sg.

 * @cpus: Set of cpus considered for load balancing.

 * @balance: Should we balance.

 * @sds: variable to hold the statistics for this sched_domain.

 */

static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,

			enum cpu_idle_type idle, int *sd_idle,

			const struct cpumask *cpus, int *balance,

			struct sd_lb_stats *sds)

			enum cpu_idle_type idle, const struct cpumask *cpus,

			int *balance, struct sd_lb_stats *sds)

{

	struct sched_domain *child = sd->child;

	struct sched_group *sg = sd->groups;
@@ -2843,7 +2837,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu, 


		local_group = cpumask_test_cpu(this_cpu, sched_group_cpus(sg));

		memset(&sgs, 0, sizeof(sgs));

		update_sg_lb_stats(sd, sg, this_cpu, idle, load_idx, sd_idle,

		update_sg_lb_stats(sd, sg, this_cpu, idle, load_idx,

				local_group, cpus, balance, &sgs);



		if (local_group && !(*balance))
@@ -3095,7 +3089,6 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu, 
 * @imbalance: Variable which stores amount of weighted load which should

 *		be moved to restore balance/put a group to idle.

 * @idle: The idle status of this_cpu.

 * @sd_idle: The idleness of sd

 * @cpus: The set of CPUs under consideration for load-balancing.

 * @balance: Pointer to a variable indicating if this_cpu

 *	is the appropriate cpu to perform load balancing at this_level.
@@ -3108,7 +3101,7 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu, 
static struct sched_group *

find_busiest_group(struct sched_domain *sd, int this_cpu,

		   unsigned long *imbalance, enum cpu_idle_type idle,

		   int *sd_idle, const struct cpumask *cpus, int *balance)

		   const struct cpumask *cpus, int *balance)

{

	struct sd_lb_stats sds;
@@ -3118,8 +3111,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, 
	 * Compute the various statistics relavent for load balancing at

	 * this level.

	 */

	update_sd_lb_stats(sd, this_cpu, idle, sd_idle, cpus,

					balance, &sds);

	update_sd_lb_stats(sd, this_cpu, idle, cpus, balance, &sds);



	/* Cases where imbalance does not exist from POV of this_cpu */

	/* 1) this_cpu is not the appropriate cpu to perform load balancing
@@ -3255,7 +3247,7 @@ find_busiest_queue(struct sched_domain *sd, struct sched_group *group, 
/* Working cpumask for load_balance and load_balance_newidle. */

static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);



static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle,

static int need_active_balance(struct sched_domain *sd, int idle,

			       int busiest_cpu, int this_cpu)

{

	if (idle == CPU_NEWLY_IDLE) {
@@ -3287,10 +3279,6 @@ static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle, 
		 * move_tasks() will succeed.  ld_moved will be true and this

		 * active balance code will not be triggered.

		 */

		if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&

		    !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))

			return 0;



		if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)

			return 0;

	}
@@ -3308,7 +3296,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, 
			struct sched_domain *sd, enum cpu_idle_type idle,

			int *balance)

{

	int ld_moved, all_pinned = 0, active_balance = 0, sd_idle = 0;

	int ld_moved, all_pinned = 0, active_balance = 0;

	struct sched_group *group;

	unsigned long imbalance;

	struct rq *busiest;
@@ -3317,20 +3305,10 @@ static int load_balance(int this_cpu, struct rq *this_rq, 


	cpumask_copy(cpus, cpu_active_mask);



	/*

	 * When power savings policy is enabled for the parent domain, idle

	 * sibling can pick up load irrespective of busy siblings. In this case,

	 * let the state of idle sibling percolate up as CPU_IDLE, instead of

	 * portraying it as CPU_NOT_IDLE.

	 */

	if (idle != CPU_NOT_IDLE && sd->flags & SD_SHARE_CPUPOWER &&

	    !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))

		sd_idle = 1;



	schedstat_inc(sd, lb_count[idle]);



redo:

	group = find_busiest_group(sd, this_cpu, &imbalance, idle, &sd_idle,

	group = find_busiest_group(sd, this_cpu, &imbalance, idle,

				   cpus, balance);



	if (*balance == 0)
@@ -3392,8 +3370,7 @@ redo: 
		if (idle != CPU_NEWLY_IDLE)

			sd->nr_balance_failed++;



		if (need_active_balance(sd, sd_idle, idle, cpu_of(busiest),

					this_cpu)) {

		if (need_active_balance(sd, idle, cpu_of(busiest), this_cpu)) {

			raw_spin_lock_irqsave(&busiest->lock, flags);



			/* don't kick the active_load_balance_cpu_stop,
@@ -3448,10 +3425,6 @@ redo: 
			sd->balance_interval *= 2;

	}



	if (!ld_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER &&

	    !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))

		ld_moved = -1;



	goto out;



out_balanced:
@@ -3465,10 +3438,6 @@ out_one_pinned: 
			(sd->balance_interval < sd->max_interval))

		sd->balance_interval *= 2;



	if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&

	    !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))

		ld_moved = -1;

	else

	ld_moved = 0;

out:

	return ld_moved;

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