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Commit b7bb4c9b authored by Gautham R Shenoy's avatar Gautham R Shenoy Committed by Ingo Molnar
Browse files

sched: Add comments to find_busiest_group() function 



Impact: cleanup

Add /** style comments around find_busiest_group(). Also add a few
explanatory comments.

This concludes the find_busiest_group() cleanup. The function is
now down to 72 lines from the original 313 lines.

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: <20090325091427.13992.18933.stgit@sofia.in.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent c071df18

kernel/sched.c

+42 −8
Original line number Diff line number Diff line
@@ -3676,10 +3676,30 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu, 
}

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



/*

 * find_busiest_group finds and returns the busiest CPU group within the

 * domain. It calculates and returns the amount of weighted load which

 * should be moved to restore balance via the imbalance parameter.

/**

 * find_busiest_group - Returns the busiest group within the sched_domain

 * if there is an imbalance. If there isn't an imbalance, and

 * the user has opted for power-savings, it returns a group whose

 * CPUs can be put to idle by rebalancing those tasks elsewhere, if

 * such a group exists.

 *

 * Also calculates the amount of weighted load which should be moved

 * to restore balance.

 *

 * @sd: The sched_domain whose busiest group is to be returned.

 * @this_cpu: The cpu for which load balancing is currently being performed.

 * @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.

 *

 * Returns:	- the busiest group if imbalance exists.

 *		- If no imbalance and user has opted for power-savings balance,

 *		   return the least loaded group whose CPUs can be

 *		   put to idle by rebalancing its tasks onto our group.

 */

static struct sched_group *

find_busiest_group(struct sched_domain *sd, int this_cpu,
@@ -3697,17 +3717,31 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, 
	update_sd_lb_stats(sd, this_cpu, idle, sd_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

	 *    at this level.

	 * 2) There is no busy sibling group to pull from.

	 * 3) This group is the busiest group.

	 * 4) This group is more busy than the avg busieness at this

	 *    sched_domain.

	 * 5) The imbalance is within the specified limit.

	 * 6) Any rebalance would lead to ping-pong

	 */

	if (balance && !(*balance))

		goto ret;



	if (!sds.busiest || sds.this_load >= sds.max_load

		|| sds.busiest_nr_running == 0)

	if (!sds.busiest || sds.busiest_nr_running == 0)

		goto out_balanced;



	if (sds.this_load >= sds.max_load)

		goto out_balanced;



	sds.avg_load = (SCHED_LOAD_SCALE * sds.total_load) / sds.total_pwr;



	if (sds.this_load >= sds.avg_load ||

			100*sds.max_load <= sd->imbalance_pct * sds.this_load)

	if (sds.this_load >= sds.avg_load)

		goto out_balanced;



	if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load)

		goto out_balanced;



	sds.busiest_load_per_task /= sds.busiest_nr_running;