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Commit dbc523a3 authored by Gautham R Shenoy's avatar Gautham R Shenoy Committed by Ingo Molnar
Browse files

sched: Create a helper function to calculate imbalance 



Move all the imbalance calculation out of find_busiest_group()
through this helper function.

With this change, the structure of find_busiest_group() will be
as follows:

- update_sched_domain_statistics.

- check if imbalance exits.

- update imbalance and return busiest.

Signed-off-by: default avatarGautham R Shenoy <ego@in.ibm.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "Balbir Singh" <balbir@in.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: "Dhaval Giani" <dhaval@linux.vnet.ibm.com>
Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Cc: "Vaidyanathan Srinivasan" <svaidy@linux.vnet.ibm.com>
LKML-Reference: <20090325091411.13992.43293.stgit@sofia.in.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2e6f44ae

kernel/sched.c

+45 −33
Original line number Diff line number Diff line
@@ -3549,6 +3549,47 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds, 
	if (pwr_move > pwr_now)

		*imbalance = sds->busiest_load_per_task;

}



/**

 * calculate_imbalance - Calculate the amount of imbalance present within the

 *			 groups of a given sched_domain during load balance.

 * @sds: statistics of the sched_domain whose imbalance is to be calculated.

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

 * @imbalance: The variable to store the imbalance.

 */

static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,

		unsigned long *imbalance)

{

	unsigned long max_pull;

	/*

	 * In the presence of smp nice balancing, certain scenarios can have

	 * max load less than avg load(as we skip the groups at or below

	 * its cpu_power, while calculating max_load..)

	 */

	if (sds->max_load < sds->avg_load) {

		*imbalance = 0;

		return fix_small_imbalance(sds, this_cpu, imbalance);

	}



	/* Don't want to pull so many tasks that a group would go idle */

	max_pull = min(sds->max_load - sds->avg_load,

			sds->max_load - sds->busiest_load_per_task);



	/* How much load to actually move to equalise the imbalance */

	*imbalance = min(max_pull * sds->busiest->__cpu_power,

		(sds->avg_load - sds->this_load) * sds->this->__cpu_power)

			/ SCHED_LOAD_SCALE;



	/*

	 * if *imbalance is less than the average load per runnable task

	 * there is no gaurantee that any tasks will be moved so we'll have

	 * a think about bumping its value to force at least one task to be

	 * moved

	 */

	if (*imbalance < sds->busiest_load_per_task)

		return fix_small_imbalance(sds, this_cpu, imbalance);



}

/******* find_busiest_group() helpers end here *********************/



/*
@@ -3562,7 +3603,6 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, 
		   int *sd_idle, const struct cpumask *cpus, int *balance)

{

	struct sd_lb_stats sds;

	unsigned long max_pull;



	memset(&sds, 0, sizeof(sds));
@@ -3605,36 +3645,8 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, 
	if (sds.max_load <= sds.busiest_load_per_task)

		goto out_balanced;



	/*

	 * In the presence of smp nice balancing, certain scenarios can have

	 * max load less than avg load(as we skip the groups at or below

	 * its cpu_power, while calculating max_load..)

	 */

	if (sds.max_load < sds.avg_load) {

		*imbalance = 0;

		fix_small_imbalance(&sds, this_cpu, imbalance);

		goto ret_busiest;

	}



	/* Don't want to pull so many tasks that a group would go idle */

	max_pull = min(sds.max_load - sds.avg_load,

			sds.max_load - sds.busiest_load_per_task);



	/* How much load to actually move to equalise the imbalance */

	*imbalance = min(max_pull * sds.busiest->__cpu_power,

			(sds.avg_load - sds.this_load) * sds.this->__cpu_power)

			/ SCHED_LOAD_SCALE;



	/*

	 * if *imbalance is less than the average load per runnable task

	 * there is no gaurantee that any tasks will be moved so we'll have

	 * a think about bumping its value to force at least one task to be

	 * moved

	 */

	if (*imbalance < sds.busiest_load_per_task)

		fix_small_imbalance(&sds, this_cpu, imbalance);



ret_busiest:

	/* Looks like there is an imbalance. Compute it */

	calculate_imbalance(&sds, this_cpu, imbalance);

	return sds.busiest;



out_balanced: