sched/topology: Remove the ::smt_gain field from 'struct sched_domain'

::smt_gain is used to compute the capacity of CPUs of a SMT core with the
constraint 1 < ::smt_gain < 2 in order to be able to compute number of CPUs
per core. The field has_free_capacity of struct numa_stat, which was the
last user of this computation of number of CPUs per core, has been removed
by:

  2d4056f ("sched/numa: Remove numa_has_capacity()")

We can now remove this constraint on core capacity and use the defautl value
SCHED_CAPACITY_SCALE for SMT CPUs. With this remove, SCHED_CAPACITY_SCALE
becomes the maximum compute capacity of CPUs on every systems. This should
help to simplify some code and remove fields like rd->max_cpu_capacity

Furthermore, arch_scale_cpu_capacity() is used with a NULL sd in several other
places in the code when it wants the capacity of a CPUs to scale
some metrics like in pelt, deadline or schedutil. In case on SMT, the value
returned is not the capacity of SMT CPUs but default SCHED_CAPACITY_SCALE.

So remove it.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1535548752-4434-4-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/topology.h

@@ -89,7 +89,6 @@ struct sched_domain {
 	unsigned int newidle_idx;
 	unsigned int wake_idx;
 	unsigned int forkexec_idx;
-	unsigned int smt_gain;
 
 	int nohz_idle;			/* NOHZ IDLE status */
 	int flags;			/* See SD_* */

kernel/sched/sched.h

@@ -1864,9 +1864,6 @@ unsigned long arch_scale_freq_capacity(int cpu)
 static __always_inline
 unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 {
-	if (sd && (sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
-		return sd->smt_gain / sd->span_weight;
-
 	return SCHED_CAPACITY_SCALE;
 }
 #endif

kernel/sched/topology.c

@@ -1133,7 +1133,6 @@ sd_init(struct sched_domain_topology_level *tl,
 
 		.last_balance		= jiffies,
 		.balance_interval	= sd_weight,
-		.smt_gain		= 0,
 		.max_newidle_lb_cost	= 0,
 		.next_decay_max_lb_cost	= jiffies,
 		.child			= child,
@@ -1164,7 +1163,6 @@ sd_init(struct sched_domain_topology_level *tl,
 
 	if (sd->flags & SD_SHARE_CPUCAPACITY) {
 		sd->imbalance_pct = 110;
-		sd->smt_gain = 1178; /* ~15% */
 
 	} else if (sd->flags & SD_SHARE_PKG_RESOURCES) {
 		sd->imbalance_pct = 117;