Messages in this thread Patch in this message | | | Subject | Re: [BUG] How to get real-time priority using idle priority | From | Peter Zijlstra <> | Date | Thu, 15 Jan 2009 14:16:51 +0100 |
| |
If you then fold this on top we have 3 patches, alas not along the lines that would have been pretty:
- update_min_vruntime fix - SCHED_IDLE weight change - SCHED_IDLE vs SCHED_OTHER isolation
But I guess that's life.
--- Subject: sched: fix update_min_vruntime From: Peter Zijlstra <a.p.zijlstra@chello.nl> Date: Thu Jan 15 14:13:28 CET 2009
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 <a.p.zijlstra@chello.nl> Tested-by: Mike Galbraith <efault@gmx.de> Acked-by: Mike Galbraith <efault@gmx.de> --- kernel/sched_fair.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
Index: linux-2.6/kernel/sched_fair.c =================================================================== --- linux-2.6.orig/kernel/sched_fair.c +++ linux-2.6/kernel/sched_fair.c @@ -283,7 +283,10 @@ static void update_min_vruntime(struct c struct sched_entity, run_node); - vruntime = min_vruntime(vruntime, se->vruntime); + if (!cfs_rq->curr) + vruntime = se->vruntime; + else + vruntime = min_vruntime(vruntime, se->vruntime); } cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
| |