Re: [PATCH 1/2] sched/fair: Fix how load gets propagated from cfs_rq to its sched_entity

From: Peter Zijlstra
Date: Tue May 02 2017 - 04:30:24 EST


On Tue, May 02, 2017 at 10:19:05AM +0200, Peter Zijlstra wrote:
> Can you have a play with something like the below? I suspect
> 'shares_runnable' might work for you here.

> ---
> kernel/sched/fair.c | 62 +++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 44 insertions(+), 18 deletions(-)

So something like so on top I suppose...

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3101,38 +3101,7 @@ static inline void
update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
struct cfs_rq *gcfs_rq = group_cfs_rq(se);
- long delta, load = gcfs_rq->avg.load_avg;
-
- /*
- * If the load of group cfs_rq is null, the load of the
- * sched_entity will also be null so we can skip the formula
- */
- if (load) {
- long tg_load;
-
- /* Get tg's load and ensure tg_load > 0 */
- tg_load = atomic_long_read(&gcfs_rq->tg->load_avg) + 1;
-
- /* Ensure tg_load >= load and updated with current load*/
- tg_load -= gcfs_rq->tg_load_avg_contrib;
- tg_load += load;
-
- /*
- * We need to compute a correction term in the case that the
- * task group is consuming more CPU than a task of equal
- * weight. A task with a weight equals to tg->shares will have
- * a load less or equal to scale_load_down(tg->shares).
- * Similarly, the sched_entities that represent the task group
- * at parent level, can't have a load higher than
- * scale_load_down(tg->shares). And the Sum of sched_entities'
- * load must be <= scale_load_down(tg->shares).
- */
- if (tg_load > scale_load_down(gcfs_rq->tg->shares)) {
- /* scale gcfs_rq's load into tg's shares*/
- load *= scale_load_down(gcfs_rq->tg->shares);
- load /= tg_load;
- }
- }
+ long delta, load = calc_cfs_shares(gcfs_rq, gcfs_rq->tg, shares_runnable);

delta = load - se->avg.load_avg;