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authorPaul Turner <pjt@google.com>2010-12-15 19:10:18 -0800
committerIngo Molnar <mingo@elte.hu>2010-12-19 16:36:30 +0100
commit19e5eebb8eaa5ca3ff8aa18cb57ccb7a9f67277d (patch)
tree652d43e29e101433fbb100b7af8ef0c35e420d7b /kernel
parent43365bd7ff37979d2afdccbe953299ed64a4649b (diff)
sched: Fix interactivity bug by charging unaccounted run-time on entity re-weight
Mike Galbraith reported poor interactivity[*] when the new shares distribution code was combined with autogroups. The root cause turns out to be a mis-ordering of accounting accrued execution time and shares updates. Since update_curr() is issued hierarchically, updating the parent entity weights to reflect child enqueue/dequeue results in the parent's unaccounted execution time then being accrued (vs vruntime) at the new weight as opposed to the weight present at accumulation. While this doesn't have much effect on processes with timeslices that cross a tick, it is particularly problematic for an interactive process (e.g. Xorg) which incurs many (tiny) timeslices. In this scenario almost all updates are at dequeue which can result in significant fairness perturbation (especially if it is the only thread, resulting in potential {tg->shares, MIN_SHARES} transitions). Correct this by ensuring unaccounted time is accumulated prior to manipulating an entity's weight. [*] http://xkcd.com/619/ is perversely Nostradamian here. Signed-off-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> LKML-Reference: <20101216031038.159704378@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched_fair.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 16ee398d8a4e..c62ebae65cf0 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -765,8 +765,12 @@ static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update)
static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
unsigned long weight)
{
- if (se->on_rq)
+ if (se->on_rq) {
+ /* commit outstanding execution time */
+ if (cfs_rq->curr == se)
+ update_curr(cfs_rq);
account_entity_dequeue(cfs_rq, se);
+ }
update_load_set(&se->load, weight);