sched: Add a new SD_SHARE_POWERDOMAIN for sched_domain

A new flag SD_SHARE_POWERDOMAIN is created to reflect whether groups of CPUs
in a sched_domain level can or not reach different power state. As an example,
the flag should be cleared at CPU level if groups of cores can be power gated
independently. This information can be used in the load balance decision or to
add load balancing level between group of CPUs that can power gate
independantly.
This flag is part of the topology flags that can be set by arch.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: schwidefsky@de.ibm.com
Cc: cmetcalf@tilera.com
Cc: benh@kernel.crashing.org
Cc: preeti@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1397209481-28542-5-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched.h

@@ -870,6 +870,7 @@ enum cpu_idle_type {
 #define SD_BALANCE_WAKE		0x0010  /* Balance on wakeup */
 #define SD_WAKE_AFFINE		0x0020	/* Wake task to waking CPU */
 #define SD_SHARE_CPUPOWER	0x0080	/* Domain members share cpu power */
+#define SD_SHARE_POWERDOMAIN	0x0100	/* Domain members share power domain */
 #define SD_SHARE_PKG_RESOURCES	0x0200	/* Domain members share cpu pkg resources */
 #define SD_SERIALIZE		0x0400	/* Only a single load balancing instance */
 #define SD_ASYM_PACKING		0x0800  /* Place busy groups earlier in the domain */

kernel/sched/core.c

@@ -5261,7 +5261,8 @@ static int sd_degenerate(struct sched_domain *sd)
 			 SD_BALANCE_FORK |
 			 SD_BALANCE_EXEC |
 			 SD_SHARE_CPUPOWER |
-			 SD_SHARE_PKG_RESOURCES)) {
+			 SD_SHARE_PKG_RESOURCES |
+			 SD_SHARE_POWERDOMAIN)) {
 		if (sd->groups != sd->groups->next)
 			return 0;
 	}
@@ -5292,7 +5293,8 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 				SD_BALANCE_EXEC |
 				SD_SHARE_CPUPOWER |
 				SD_SHARE_PKG_RESOURCES |
-				SD_PREFER_SIBLING);
+				SD_PREFER_SIBLING |
+				SD_SHARE_POWERDOMAIN);
 		if (nr_node_ids == 1)
 			pflags &= ~SD_SERIALIZE;
 	}
@@ -5901,6 +5903,7 @@ static int sched_domains_curr_level;
  * SD_SHARE_CPUPOWER      - describes SMT topologies
  * SD_SHARE_PKG_RESOURCES - describes shared caches
  * SD_NUMA                - describes NUMA topologies
+ * SD_SHARE_POWERDOMAIN   - describes shared power domain
  *
  * Odd one out:
  * SD_ASYM_PACKING        - describes SMT quirks
@@ -5909,7 +5912,8 @@ static int sched_domains_curr_level;
 	(SD_SHARE_CPUPOWER |		\
 	 SD_SHARE_PKG_RESOURCES |	\
 	 SD_NUMA |			\
-	 SD_ASYM_PACKING)
+	 SD_ASYM_PACKING |		\
+	 SD_SHARE_POWERDOMAIN)
 
 static struct sched_domain *
 sd_init(struct sched_domain_topology_level *tl, int cpu)