From e17036dac189dd034c092a91df56aa740db7146d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 15 Jan 2009 14:53:39 +0100 Subject: [PATCH] sched: fix update_min_vruntime Impact: fix SCHED_IDLE latency problems OK, so we have 1 running task A (which is obviously curr and the tree is equally obviously empty). 'A' nicely chugs along, doing its thing, carrying min_vruntime along as it goes. Then some whacko speed freak SCHED_IDLE task gets inserted due to SMP balancing, which is very likely far right, in that case update_curr update_min_vruntime cfs_rq->rb_leftmost := true (the crazy task sitting in a tree) vruntime = se->vruntime and voila, min_vruntime is waaay right of where it ought to be. OK, so why did I write it like that to begin with... Aah, yes. Say we've just dequeued current schedule deactivate_task(prev) dequeue_entity update_min_vruntime Then we'll set vruntime = cfs_rq->min_vruntime; we find !cfs_rq->curr, but do find someone in the tree. Then we _must_ do vruntime = se->vruntime, because vruntime = min_vruntime(vruntime := cfs_rq->min_vruntime, se->vruntime) will not advance vruntime, and cause lags the other way around (which we fixed with that initial patch: 1af5f730fc1bf7c62ec9fb2d307206e18bf40a69 (sched: more accurate min_vruntime accounting). Signed-off-by: Peter Zijlstra Tested-by: Mike Galbraith Acked-by: Mike Galbraith Cc: Signed-off-by: Ingo Molnar --- kernel/sched_fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index cdebd80..16b419b 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -283,7 +283,7 @@ static void update_min_vruntime(struct cfs_rq *cfs_rq) struct sched_entity, run_node); - if (vruntime == cfs_rq->min_vruntime) + if (!cfs_rq->curr) vruntime = se->vruntime; else vruntime = min_vruntime(vruntime, se->vruntime); -- 1.8.2.3