sched: Add SD_PREFER_LOCAL

And turn it on for NUMA and MC domains. This improves
locality in balancing decisions by keeping up to
capacity amount of tasks local before looking for idle
CPUs. (and twice the capacity if SD_POWERSAVINGS_BALANCE
is set.)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 8 insertions, 3 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ee1f88993097..b4a39bb2b4a4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -805,7 +805,7 @@ enum cpu_idle_type {
 #define SD_BALANCE_FORK         0x0008  /* Balance on fork, clone */
 #define SD_BALANCE_WAKE         0x0010  /* Balance on wakeup */
 #define SD_WAKE_AFFINE          0x0020  /* Wake task to waking CPU */
-
+#define SD_PREFER_LOCAL         0x0040  /* Prefer to keep tasks local to this domain */
 #define SD_SHARE_CPUPOWER       0x0080  /* Domain members share cpu power */
 #define SD_POWERSAVINGS_BALANCE 0x0100  /* Balance for power savings */
 #define SD_SHARE_PKG_RESOURCES  0x0200  /* Domain members share cpu pkg resources */
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 936ab2b37683..a6614b0242a9 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -129,6 +129,7 @@ int arch_update_cpu_topology(void);
                                 | 1*SD_BALANCE_FORK                     \
                                 | 1*SD_BALANCE_WAKE                     \
                                 | 1*SD_WAKE_AFFINE                      \
+                                | 1*SD_PREFER_LOCAL                     \
                                 | 0*SD_SHARE_CPUPOWER                   \
                                 | 1*SD_SHARE_PKG_RESOURCES              \
                                 | 0*SD_SERIALIZE                        \
@@ -161,6 +162,7 @@ int arch_update_cpu_topology(void);
                                 | 1*SD_BALANCE_FORK                     \
                                 | 1*SD_BALANCE_WAKE                     \
                                 | 1*SD_WAKE_AFFINE                      \
+                                | 1*SD_PREFER_LOCAL                     \
                                 | 0*SD_SHARE_CPUPOWER                   \
                                 | 0*SD_SHARE_PKG_RESOURCES              \
                                 | 0*SD_SERIALIZE                        \
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 280892e9d85e..a37f311f436e 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1360,7 +1360,7 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int flags)
                  * If power savings logic is enabled for a domain, see if we
                  * are not overloaded, if so, don't balance wider.
                  */
-                if (tmp->flags & SD_POWERSAVINGS_BALANCE) {
+                if (tmp->flags & (SD_POWERSAVINGS_BALANCE|SD_PREFER_LOCAL)) {
                         unsigned long power = 0;
                         unsigned long nr_running = 0;
                         unsigned long capacity;
@@ -1373,7 +1373,10 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int flags)
 
                         capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
 
-                        if (nr_running/2 < capacity)
+                        if (tmp->flags & SD_POWERSAVINGS_BALANCE)
+                                nr_running /= 2;
+
+                        if (nr_running < capacity)
                                 break;
                 }