[PATCH v3 05/13] sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag

[Morten Rasmussen <morten.rasmussen@arm.com>]

Add a topology flag to the sched_domain hierarchy indicating the lowest
domain level where the full range of cpu capacities is represented by
the domain members for asymmetric capacity topologies (e.g. ARM
big.LITTLE).

The flag is intended to indicate that extra care should be taken when
placing tasks on cpus and this level spans all the different types of
cpus found in the system (no need to look further up the domain
hierarchy). This information is currently only available through
iterating through the capacities of all the cpus at parent levels in the
sched_domain hierarchy.

SD 2      [  0      1      2      3]  SD_ASYM_CPUCAPACITY

SD 1      [  0      1] [   2      3]  !SD_ASYM_CPUCAPACITY

cpu:         0      1      2      3
capacity:  756    756   1024   1024

If the topology in the example above is duplicated to create an eight
cpu example with third sched_domain level on top (SD 3), this level
should not have the flag set (!SD_ASYM_CPUCAPACITY) as its two group
would both have all cpu capacities represented within them.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 include/linux/sched.h | 1 +
 kernel/sched/core.c   | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 930784dd7cd8..4e0c47af9b05 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1021,6 +1021,7 @@ extern void wake_up_q(struct wake_q_head *head);
 #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_ASYM_CPUCAPACITY	0x0040  /* Groups have different max cpu capacities */
 #define SD_SHARE_CPUCAPACITY	0x0080	/* Domain members share cpu capacity */
 #define SD_SHARE_POWERDOMAIN	0x0100	/* Domain members share power domain */
 #define SD_SHARE_PKG_RESOURCES	0x0200	/* Domain members share cpu pkg resources */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0a40beb46841..1a22fc9e3788 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5692,6 +5692,7 @@ static int sd_degenerate(struct sched_domain *sd)
 			 SD_BALANCE_FORK |
 			 SD_BALANCE_EXEC |
 			 SD_SHARE_CPUCAPACITY |
+			 SD_ASYM_CPUCAPACITY |
 			 SD_SHARE_PKG_RESOURCES |
 			 SD_SHARE_POWERDOMAIN)) {
 		if (sd->groups != sd->groups->next)
@@ -5722,6 +5723,7 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 				SD_BALANCE_NEWIDLE |
 				SD_BALANCE_FORK |
 				SD_BALANCE_EXEC |
+				SD_ASYM_CPUCAPACITY |
 				SD_SHARE_CPUCAPACITY |
 				SD_SHARE_PKG_RESOURCES |
 				SD_PREFER_SIBLING |
@@ -6336,14 +6338,16 @@ static int sched_domains_curr_level;
  * SD_NUMA                - describes NUMA topologies
  * SD_SHARE_POWERDOMAIN   - describes shared power domain
  *
- * Odd one out:
+ * Odd ones out:
  * SD_ASYM_PACKING        - describes SMT quirks
+ * SD_ASYM_CPUCAPACITY    - describes mixed capacity topologies
  */
 #define TOPOLOGY_SD_FLAGS		\
 	(SD_SHARE_CPUCAPACITY |		\
 	 SD_SHARE_PKG_RESOURCES |	\
 	 SD_NUMA |			\
 	 SD_ASYM_PACKING |		\
+	 SD_ASYM_CPUCAPACITY |		\
 	 SD_SHARE_POWERDOMAIN)
 
 static struct sched_domain *
-- 
1.9.1