From 19e5eebb8eaa5ca3ff8aa18cb57ccb7a9f67277d Mon Sep 17 00:00:00 2001 From: Paul Turner Date: Wed, 15 Dec 2010 19:10:18 -0800 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra Cc: Mike Galbraith Cc: Linus Torvalds LKML-Reference: <20101216031038.159704378@google.com> Signed-off-by: Ingo Molnar --- kernel/sched_fair.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) 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);