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authorVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>2008-12-18 23:26:29 +0530
committerIngo Molnar <mingo@elte.hu>2008-12-19 09:21:52 +0100
commit7eb52dfa70dbf5232b5b83ec4357e6bebaa8fde8 (patch)
treedfff4d1dcf62e992717f0934961f4557896d4945 /kernel
parent7a09b1a27b1e5a4957e4af9951420fea02c44fba (diff)
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sched: bias task wakeups to preferred semi-idle packages
Impact: tweak task wakeup to save power more agressively Preferred wakeup cpu (from a semi idle package) has been nominated in find_busiest_group() in the previous patch. Use this information in sched_mc_preferred_wakeup_cpu in function wake_idle() to bias task wakeups if the following conditions are satisfied: - The present cpu that is trying to wakeup the process is idle and waking the target process on this cpu will potentially wakeup a completely idle package - The previous cpu on which the target process ran is also idle and hence selecting the previous cpu may wakeup a semi idle cpu package - The task being woken up is allowed to run in the nominated cpu (cpu affinity and restrictions) Basically if both the current cpu and the previous cpu on which the task ran is idle, select the nominated cpu from semi idle cpu package for running the new task that is waking up. Cache hotness is considered since the actual biasing happens in wake_idle() only if the application is cache cold. This technique will effectively move short running bursty jobs in a mostly idle system. Wakeup biasing for power savings gets automatically disabled if system utilisation increases due to the fact that the probability of finding both this_cpu and prev_cpu idle decreases. 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')
-rw-r--r--kernel/sched_fair.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 08ffffd..36b5e34 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1026,6 +1026,24 @@ static int wake_idle(int cpu, struct task_struct *p)
{
struct sched_domain *sd;
int i;
+ unsigned int chosen_wakeup_cpu;
+ int this_cpu;
+
+ /*
+ * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
+ * are idle and this is not a kernel thread and this task's affinity
+ * allows it to be moved to preferred cpu, then just move!
+ */
+
+ this_cpu = smp_processor_id();
+ chosen_wakeup_cpu =
+ cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;
+
+ if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP &&
+ idle_cpu(cpu) && idle_cpu(this_cpu) &&
+ p->mm && !(p->flags & PF_KTHREAD) &&
+ cpu_isset(chosen_wakeup_cpu, p->cpus_allowed))
+ return chosen_wakeup_cpu;
/*
* If it is idle, then it is the best cpu to run this task.