sched: Optimize the !power_savings_balance during fbg()

Impact: cleanup, micro-optimization

We don't need to perform power_savings balance if either the
cpu is NOT_IDLE or if the sched_domain doesn't contain the
SD_POWERSAVINGS_BALANCE flag set.

Currently, we check for these conditions multiple number of
times, even though these variables don't change over the scope
of find_busiest_group().

Check once, and store the value in the already exiting
"power_savings_balance" variable.
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Peter 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: <20090325091417.13992.2657.stgit@sofia.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -3386,8 +3386,17 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 	int load_idx;
 
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+	/*
+	 * Busy processors will not participate in power savings
+	 * balance.
+	 */
+	if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+		sds->power_savings_balance = 0;
+	else {
 		sds->power_savings_balance = 1;
 		sds->min_nr_running = ULONG_MAX;
+		sds->leader_nr_running = 0;
+	}
 #endif
 	load_idx = get_sd_load_idx(sd, idle);
 
@@ -3422,12 +3431,8 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 		}
 
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-		/*
-		 * Busy processors will not participate in power savings
-		 * balance.
-		 */
-		if (idle == CPU_NOT_IDLE ||
-				!(sd->flags & SD_POWERSAVINGS_BALANCE))
+
+		if (!sds->power_savings_balance)
 			goto group_next;
 
 		/*
@@ -3651,7 +3656,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 
 out_balanced:
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-	if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+	if (!sds.power_savings_balance)
 		goto ret;
 
 	if (sds.this != sds.group_leader || sds.group_leader == sds.group_min)