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authorVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>2008-12-18 23:26:22 +0530
committerIngo Molnar <mingo@elte.hu>2008-12-19 09:21:50 +0100
commit7a09b1a27b1e5a4957e4af9951420fea02c44fba (patch)
tree8b13c8025bbf2bd8fc60e6590e54c1036709b0da /kernel/sched.c
parentd5679bd11916eba5c8ee9033003e1a5ce56ece9a (diff)
sched: nominate preferred wakeup cpu
Impact: extend load-balancing code (no change in behavior yet) When the system utilisation is low and more cpus are idle, then the process waking up from sleep should prefer to wakeup an idle cpu from semi-idle cpu package (multi core package) rather than a completely idle cpu package which would waste power. Use the sched_mc balance logic in find_busiest_group() to nominate a preferred wakeup cpu. This info can be stored in appropriate sched_domain, but updating this info in all copies of sched_domain is not practical. Hence this information is stored in root_domain struct which is one copy per partitioned sched domain. The root_domain can be accessed from each cpu's runqueue and there is one copy per partitioned sched domain. Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 94b9d11e331..c1b8b3031eb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -509,6 +509,14 @@ struct root_domain {
#ifdef CONFIG_SMP
struct cpupri cpupri;
#endif
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+ /*
+ * Preferred wake up cpu nominated by sched_mc balance that will be
+ * used when most cpus are idle in the system indicating overall very
+ * low system utilisation. Triggered at POWERSAVINGS_BALANCE_WAKEUP(2)
+ */
+ unsigned int sched_mc_preferred_wakeup_cpu;
+#endif
};
/*
@@ -3384,6 +3392,10 @@ out_balanced:
if (this == group_leader && group_leader != group_min) {
*imbalance = min_load_per_task;
+ if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
+ cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
+ first_cpu(group_leader->cpumask);
+ }
return group_min;
}
#endif