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Subject[PATCH 13/15] sched,fair: ramp up task_se_h_weight quickly
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The code in update_cfs_group / calc_group_shares has some logic to
quickly ramp up the load when a task has just started running in a
cgroup, in order to get sane values for the cgroup se->load.weight.

This code adds a similar hack to task_se_h_weight.

However, THIS CODE IS WRONG, since it does not do things hierarchically.

I am wondering a few things here:
1) Should I have something similar to the logic in calc_group_shares
in update_cfs_rq_h_load?
2) If so, should I also use that fast-ramp-up value for task_h_load,
to prevent the load balancer from thinking it is moving zero weight
tasks around?
3) If update_cfs_rq_h_load is the wrong place, where should I be
calculating a hierarchical group weight value, instead?

Not-yet-signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Rik van Riel <riel@surriel.com>
---
kernel/sched/fair.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 84481c9ca51d..1049f2f4ae55 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7690,6 +7690,7 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)

static unsigned long task_se_h_weight(struct sched_entity *se)
{
+ unsigned long group_load;
struct cfs_rq *cfs_rq;

if (!task_se_in_cgroup(se))
@@ -7698,8 +7699,12 @@ static unsigned long task_se_h_weight(struct sched_entity *se)
cfs_rq = group_cfs_rq_of_parent(se);
update_cfs_rq_h_load(cfs_rq);

+ /* Ramp up quickly to keep h_weight sane. */
+ group_load = max(scale_load_down(se->parent->load.weight),
+ cfs_rq->h_load);
+
/* Reduce the load.weight by the h_load of the group the task is in. */
- return (cfs_rq->h_load * se->load.weight) >> SCHED_FIXEDPOINT_SHIFT;
+ return (group_load * se->load.weight) >> SCHED_FIXEDPOINT_SHIFT;
}

static unsigned long task_se_h_load(struct sched_entity *se)
--
2.20.1
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