[tip: sched/core] sched/fair: Revise comment about lb decision matrix

[tip-bot2 for Tao Zhou]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     a658353167bf2ea6052cee071dbcc13e0f229dc9
Gitweb:        https://git.kernel.org/tip/a658353167bf2ea6052cee071dbcc13e0f229dc9
Author:        Tao Zhou <tao.zhou@xxxxxxxxx>
AuthorDate:    Fri, 15 Apr 2022 17:55:04 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 22 Apr 2022 12:14:08 +02:00

sched/fair: Revise comment about lb decision matrix

If busiest group type is group_misfit_task, the local
group type must be group_has_spare according to below
code in update_sd_pick_busiest():

  if (sgs->group_type == group_misfit_task &&
      (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) ||
       sds->local_stat.group_type != group_has_spare))
	   return false;

group type imbalanced and overloaded and fully_busy are filtered in here.
misfit and asym are filtered before in update_sg_lb_stats().
So, change the decision matrix to:

  busiest \ local has_spare fully_busy misfit asym imbalanced overloaded
  has_spare        nr_idle   balanced   N/A    N/A  balanced   balanced
  fully_busy       nr_idle   nr_idle    N/A    N/A  balanced   balanced
  misfit_task      force     N/A        N/A    N/A  *N/A*      *N/A*
  asym_packing     force     force      N/A    N/A  force      force
  imbalanced       force     force      N/A    N/A  force      force
  overloaded       force     force      N/A    N/A  force      avg_load

Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()")
Signed-off-by: Tao Zhou <tao.zhou@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20220415095505.7765-1-tao.zhou@xxxxxxxxx
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3eba0dc..4c42012 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9496,7 +9496,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
  * busiest \ local has_spare fully_busy misfit asym imbalanced overloaded
  * has_spare        nr_idle   balanced   N/A    N/A  balanced   balanced
  * fully_busy       nr_idle   nr_idle    N/A    N/A  balanced   balanced
- * misfit_task      force     N/A        N/A    N/A  force      force
+ * misfit_task      force     N/A        N/A    N/A  N/A        N/A
  * asym_packing     force     force      N/A    N/A  force      force
  * imbalanced       force     force      N/A    N/A  force      force
  * overloaded       force     force      N/A    N/A  force      avg_load