[RFC][PATCH 14/14] sched/fair: More accurate async detach

[Peter Zijlstra]

The problem with the overestimate is that it will subtract too big a
value from the load_sum, thereby pushing it down further than it ought
to go. Since runnable_load_avg is not subject to a similar 'force',
this results in the occasional 'runnable_load > load' situation.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
 kernel/sched/fair.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3469,6 +3469,7 @@ update_cfs_rq_load_avg(u64 now, struct c
 
        if (cfs_rq->removed.nr) {
                unsigned long r;
+               u32 divider = LOAD_AVG_MAX - 1024 + sa->period_contrib;
 
                raw_spin_lock(&cfs_rq->removed.lock);
                swap(cfs_rq->removed.util_avg, removed_util);
@@ -3477,17 +3478,13 @@ update_cfs_rq_load_avg(u64 now, struct c
                cfs_rq->removed.nr = 0;
                raw_spin_unlock(&cfs_rq->removed.lock);
 
-               /*
-                * The LOAD_AVG_MAX for _sum is a slight over-estimate,
-                * which is safe due to sub_positive() clipping at 0.
-                */
                r = removed_load;
                sub_positive(&sa->load_avg, r);
-               sub_positive(&sa->load_sum, r * LOAD_AVG_MAX);
+               sub_positive(&sa->load_sum, r * divider);
 
                r = removed_util;
                sub_positive(&sa->util_avg, r);
-               sub_positive(&sa->util_sum, r * LOAD_AVG_MAX);
+               sub_positive(&sa->util_sum, r * divider);
 
                add_tg_cfs_propagate(cfs_rq, -(long)removed_runnable_sum);