sched: add SD_BALANCE_NEWIDLE at MC and CPU level for sched_mc>0

Impact: change task balancing to save power more agressively

Add SD_BALANCE_NEWIDLE flag at MC level and CPU level
if sched_mc is set.  This helps power savings and
will not affect performance when sched_mc=0

Ingo and Mike Galbraith have optimised the SD flags by
removing SD_BALANCE_NEWIDLE at MC and CPU level.  This
helps performance but hurts power savings since this
slows down task consolidation by reducing the number
of times load_balance is run.

    sched: fine-tune SD_MC_INIT
        commit 14800984706bf6936bbec5187f736e928be5c218
        Author: Mike Galbraith <efault@gmx.de>
        Date:   Fri Nov 7 15:26:50 2008 +0100

    sched: re-tune balancing -- revert
        commit 9fcd18c9e63e325dbd2b4c726623f760788d5aa8
        Author: Ingo Molnar <mingo@elte.hu>
        Date:   Wed Nov 5 16:52:08 2008 +0100

This patch selectively enables SD_BALANCE_NEWIDLE flag
only when sched_mc is set to 1 or 2.  This helps power savings
by task consolidation and also does not hurt performance at
sched_mc=0 where all power saving optimisations are turned off.

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>

2 files changed, 17 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a96726658eca..5a933d925473 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -792,6 +792,19 @@ static inline int sd_balance_for_package_power(void)
         return 0;
 }
 
+/*
+ * Optimise SD flags for power savings:
+ * SD_BALANCE_NEWIDLE helps agressive task consolidation and power savings.
+ * Keep default SD flags if sched_{smt,mc}_power_saving=0
+ */
+
+static inline int sd_power_saving_flags(void)
+{
+        if (sched_mc_power_savings | sched_smt_power_savings)
+                return SD_BALANCE_NEWIDLE;
+
+        return 0;
+}
 
 struct sched_group {
         struct sched_group *next;       /* Must be a circular list */
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 0ce7c0dac06c..e632d29f0544 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -125,7 +125,8 @@ int arch_update_cpu_topology(void);
                                 | SD_WAKE_AFFINE        \
                                 | SD_WAKE_BALANCE       \
                                 | SD_SHARE_PKG_RESOURCES\
-                                | sd_balance_for_mc_power(),\
+                                | sd_balance_for_mc_power()\
+                                | sd_power_saving_flags(),\
         .last_balance           = jiffies,              \
         .balance_interval       = 1,                    \
 }
@@ -150,7 +151,8 @@ int arch_update_cpu_topology(void);
                                 | SD_BALANCE_FORK       \
                                 | SD_WAKE_AFFINE        \
                                 | SD_WAKE_BALANCE       \
-                                | sd_balance_for_package_power(),\
+                                | sd_balance_for_package_power()\
+                                | sd_power_saving_flags(),\
         .last_balance           = jiffies,              \
         .balance_interval       = 1,                    \
 }