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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 934f615cccebeb5044455dcdfd0b0e9d57221b92..71e8dcaf2c790eefc3ca429466061e419eb8b9d7 100644 (file)
--- a/kernel/sched.c
+++ b/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)
-       sds->power_savings_balance = 1;
-       sds->min_nr_running = ULONG_MAX;
+       /*
+        * 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)