sched/fair: Fix the group_capacity computation

/*

 * Compute the group capacity.

 *

 * For now the capacity is simply the number of power units in the group_power.

 * A power unit represents a full core.

 *

 * This has an issue where N*frac(smt_power) >= 1, in that case we'll see extra

 * 'cores' that aren't actually there.

 * Avoid the issue where N*frac(smt_power) >= 1 creates 'phantom' cores by

 * first dividing out the smt factor and computing the actual number of cores

 * and limit power unit capacity with that.

 */

static inline int sg_capacity(struct lb_env *env, struct sched_group *group)

{

	unsigned int capacity, smt, cpus;

	unsigned int power, power_orig;

	power = group->sgp->power;

	power_orig = group->sgp->power_orig;

	cpus = group->group_weight;

	unsigned int power = group->sgp->power;

	unsigned int capacity = DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE);

	/* smt := ceil(cpus / power), assumes: 1 < smt_power < 2 */

	smt = DIV_ROUND_UP(SCHED_POWER_SCALE * cpus, power_orig);

	capacity = cpus / smt; /* cores */

	capacity = min_t(unsigned, capacity, DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE));

	if (!capacity)

		capacity = fix_small_capacity(env->sd, group);