Merge tag 'sched-urgent-2021-06-30' of git://git.kernel.org/pub/scm/l…

…inux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:

 - Fix a small inconsistency (bug) in load tracking, caught by a new
   warning that several people reported.

 - Flip CONFIG_SCHED_CORE to default-disabled, and update the Kconfig
   help text.

* tag 'sched-urgent-2021-06-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Disable CONFIG_SCHED_CORE by default
  sched/fair: Ensure _sum and _avg values stay consistent

kernel/Kconfig.preempt

@@ -102,7 +102,6 @@ config PREEMPT_DYNAMIC
 
 config SCHED_CORE
 	bool "Core Scheduling for SMT"
-	default y
 	depends on SCHED_SMT
 	help
 	  This option permits Core Scheduling, a means of coordinated task
@@ -115,7 +114,8 @@ config SCHED_CORE
 	   - mitigation of some (not all) SMT side channels;
 	   - limiting SMT interference to improve determinism and/or performance.
 
-	  SCHED_CORE is default enabled when SCHED_SMT is enabled -- when
-	  unused there should be no impact on performance.
+	  SCHED_CORE is default disabled. When it is enabled and unused,
+	  which is the likely usage by Linux distributions, there should
+	  be no measurable impact on performance.
 
 

kernel/sched/fair.c

@@ -3685,15 +3685,15 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 
 		r = removed_load;
 		sub_positive(&sa->load_avg, r);
-		sub_positive(&sa->load_sum, r * divider);
+		sa->load_sum = sa->load_avg * divider;
 
 		r = removed_util;
 		sub_positive(&sa->util_avg, r);
-		sub_positive(&sa->util_sum, r * divider);
+		sa->util_sum = sa->util_avg * divider;
 
 		r = removed_runnable;
 		sub_positive(&sa->runnable_avg, r);
-		sub_positive(&sa->runnable_sum, r * divider);
+		sa->runnable_sum = sa->runnable_avg * divider;
 
 		/*
 		 * removed_runnable is the unweighted version of removed_load so we