Messages in this thread Patch in this message | | | Date | Wed, 10 Feb 2016 13:48:48 +0100 | From | luca abeni <> | Subject | Re: [PATCH 1/2] sched/deadline: add per rq tracking of admitted bandwidth |
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Hi,
On Wed, 10 Feb 2016 11:32:58 +0000 Juri Lelli <juri.lelli@arm.com> wrote: [...] > From 62f70ca3051672dce209e8355cf5eddc9d825c2a Mon Sep 17 00:00:00 2001 > From: Juri Lelli <juri.lelli@arm.com> > Date: Sat, 6 Feb 2016 12:41:09 +0000 > Subject: [PATCH 1/2] sched/deadline: add per rq tracking of admitted > bandwidth > > Currently SCHED_DEADLINE scheduling policy tracks bandwidth of tasks > that passed admission control at root_domain level only. This creates > problems when such data structure(s) are destroyed, when we > reconfigure scheduling domains for example. > > This is part one of two changes required to fix the problem. In this > patch we add per-rq tracking of admitted bandwidth. Tasks bring with > them their bandwidth contribution when they enter the system and are > enqueued for the first time. Contributions are then moved around when > migrations happen and removed when tasks die.
I think this patch actually does two different things (addressing two separate problems): 1) it introduces the tracking of per-rq utilization (used in your next patch to address the root domain issues) 2) it fixes a bug in the current utilization tracking mechanism. Currently, a task doing while(1) { switch to SCHED_DEADLINE switch to SCHED_OTHER } brings dl_b->total_bw below 0. Thanks to Juri for showing me this problem (and how to reproduce it) in a private email. This happens because when the task switches back from SCHED_DEADLINE to SCHED_OTHER, switched_from_dl() does not clear its deadline parameters (they will be cleared by the deadline timer when it fires). But dl_overflow() removes its utilization from dl_b->total_bw. When the task switches back to SCHED_DEADLINE, the if (new_bw == p->dl.dl_bw) check in dl_overflow() prevents __dl_add() from being called, and so when the task switches back to SCHED_OTHER dl_b->total_bw becomes negative.
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 9503d59..0ee0ec2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2432,7 +2432,7 @@ static int dl_overflow(struct task_struct *p, > int policy, u64 new_bw = dl_policy(policy) ? to_ratio(period, > runtime) : 0; int cpus, err = -1; > > - if (new_bw == p->dl.dl_bw) > + if (task_has_dl_policy(p) && new_bw == p->dl.dl_bw) > return 0;
This hunk actually fixes issue 2) mentioned above, so I think it should be committed in a short time (independently from the rest of the patch). And maybe is a good candidate for backporting to stable kernels?
Thanks, Luca
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