Messages in this thread Patch in this message | | | Date | Fri, 26 Jul 2013 23:50:11 +0200 | From | Peter Zijlstra <> | Subject | Re: PROBLEM: Persistent unfair sharing of a processor by auto groups in 3.11-rc2 (has twice regressed) |
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On Fri, Jul 26, 2013 at 02:24:50PM -0700, Paul Turner wrote: > On Fri, Jul 26, 2013 at 2:03 PM, Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > OK, so I have the below; however on a second look, Paul, shouldn't that > > update_cfs_shares() call be in entity_tick(), right after calling > > update_cfs_rq_blocked_load(). Because placing it in > > update_cfs_rq_blocked_load() means its now called twice on the > > enqueue/dequeue paths through: > > > > {en,de}queue_entity() > > {en,de}queue_entity_load_avg() > > update_cfs_rq_blocked_load() > > update_cfs_shares() > > Yes, I agree: placing it directly in entity_tick() would be better.
OK, how about the below then?
> [ In f269ae046 the calls to update_cfs_rq_blocked_load() were amortized > and the separate update in {en,de}queue_entity_load_avg() were > removed. ]
Right, I remember/saw that. Did you ever figure out why that regressed; as in should we look to bring some of that back?
--- Subject: sched: Ensure update_cfs_shares() is called for parents of continuously-running tasks From: Peter Zijlstra <peterz@infradead.org> Date: Fri Jul 26 23:48:42 CEST 2013
We typically update a task_group's shares within the dequeue/enqueue path. However, continuously running tasks sharing a CPU are not subject to these updates as they are only put/picked. Unfortunately, when we reverted f269ae046 (in 17bc14b7), we lost the augmenting periodic update that was supposed to account for this; resulting in a potential loss of fairness.
To fix this, re-introduce the explicit update in update_cfs_rq_blocked_load() [called via entity_tick()].
Cc: stable@kernel.org Reported-by: Max Hailperin <max@gustavus.edu> Reviewed-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> --- kernel/sched/fair.c | 1 + 1 file changed, 1 insertion(+)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2032,6 +2032,7 @@ entity_tick(struct cfs_rq *cfs_rq, struc */ update_entity_load_avg(curr, 1); update_cfs_rq_blocked_load(cfs_rq, 1); + update_cfs_shares(cfs_rq); #ifdef CONFIG_SCHED_HRTICK /*
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