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Date: Mon, 10 Aug 2015 15:10:08 +0100
From: Juri Lelli <juri.lelli@....com>
To: Wanpeng Li <kernellwp@...il.com>
CC: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"wanpeng.li@...mail.com" <wanpeng.li@...mail.com>
Subject: Re: [PATCH] sched/deadline: fix dl bandwidth of root domain overflow
after dl task dead
On 06/08/15 09:39, Wanpeng Li wrote:
> Hi Juri,
>
Hi,
> 2015-05-06 16:14 GMT+08:00 Juri Lelli <juri.lelli@....com
> <mailto:juri.lelli@....com>>:
>
> Hi Wanpeng,
>
> I finally got to review this, sorry about the huge delay.
>
> On 07/04/2015 04:36, Wanpeng Li wrote:
> > The total used dl bandwidth of each root domain will be reset to 0 after
> > cpu hotplug when rebuild sched domains, since the call path is:
> >
> > _cpu_down
> > cpuset_cpu_inactive()
> > cpuset_update_active_cpus()
> > partition_sched_domains()
> > build_sched_domains()
> > init_rootdomain()
> > init_dl_bw()
> >
> > The bandwidth which dl task occupy will be released when dl task dead,
> > it will be minus from total used dl bandwidth of its root domain,
> > however, bandwidth overflow occurs since total used dl bandwidth is 0.
> >
>
> Right, that's a bug.
>
> > This patch fix it by attaching the bandwidth which dl task occupy to
> > the new root domain when the task is migrating since cpu hotplug, and
> > attach all the used dl bandwidth of dl tasks to the new root domain
> > when sched domains are rebuild.
> >
>
> But, I think this fix has still a couple of problems:
>
> - what happens if a DL task is simply sleeping when domains are
> reconfigured?
>
> - def_root_domain has now multiple accounting problems, as you do
> this thing even when a cpu is moved there in the cpuoff path
>
> Also, runqueue (and throttling) information are dynamic, while we
> are trying to fix a static problem. It's probably not a good idea
> mixing them.
>
> I'm not sure how (I need more time to think it through), but can
> we maybe fix this using cpuset information?
>
>
> Any ideas?
>
Yes, actually. I might have a different fix, but I'd like to play with
it a bit more as it is a bit too intrusive. Let me see if I can come
up with something that I can share.
Thanks,
- Juri
> Regards,
> Wanpeng Li
>
>
>
> Thanks,
>
> - Juri
>
> > Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com
> <mailto:wanpeng.li@...ux.intel.com>>
> > ---
> > kernel/sched/core.c | 1 +
> > kernel/sched/deadline.c | 25 +++++++++++++++++++++++++
> > kernel/sched/sched.h | 1 +
> > 3 files changed, 27 insertions(+)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 28b0d75..c940999 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -5586,6 +5586,7 @@ static void rq_attach_root(struct rq *rq,
> struct root_domain *rd)
> > rq->rd = rd;
> >
> > cpumask_set_cpu(rq->cpu, rd->span);
> > + attach_dl_bw(rq);
> > if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
> > set_rq_online(rq);
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index 5e95145..62680d7 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -224,6 +224,7 @@ static void dl_task_offline_migration(struct
> rq *rq, struct task_struct *p)
> > {
> > struct rq *later_rq = NULL;
> > bool fallback = false;
> > + struct dl_bw *dl_b;
> >
> > later_rq = find_lock_later_rq(p, rq);
> >
> > @@ -258,6 +259,11 @@ static void dl_task_offline_migration(struct
> rq *rq, struct task_struct *p)
> > set_task_cpu(p, later_rq->cpu);
> > activate_task(later_rq, p, ENQUEUE_REPLENISH);
> >
> > + dl_b = dl_bw_of(later_rq->cpu);
> > + raw_spin_lock(&dl_b->lock);
> > + __dl_add(dl_b, p->dl.dl_bw);
> > + raw_spin_unlock(&dl_b->lock);
> > +
> > if (!fallback)
> > resched_curr(later_rq);
> >
> > @@ -1776,6 +1782,25 @@ static void prio_changed_dl(struct rq *rq,
> struct task_struct *p,
> > switched_to_dl(rq, p);
> > }
> >
> > +void attach_dl_bw(struct rq *rq)
> > +{
> > + struct rb_node *next_node = rq->dl.rb_leftmost;
> > + struct sched_dl_entity *dl_se;
> > + struct dl_bw *dl_b;
> > +
> > + dl_b = dl_bw_of(rq->cpu);
> > + raw_spin_lock(&dl_b->lock);
> > +next_node:
> > + if (next_node) {
> > + dl_se = rb_entry(next_node, struct sched_dl_entity,
> rb_node);
> > + __dl_add(dl_b, dl_se->dl_bw);
> > + next_node = rb_next(next_node);
> > +
> > + goto next_node;
> > + }
> > + raw_spin_unlock(&dl_b->lock);
> > +}
> > +
> > const struct sched_class dl_sched_class = {
> > .next = &rt_sched_class,
> > .enqueue_task = enqueue_task_dl,
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index e0e1299..a7b1a59 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -1676,6 +1676,7 @@ extern void init_dl_rq(struct dl_rq *dl_rq);
> >
> > extern void cfs_bandwidth_usage_inc(void);
> > extern void cfs_bandwidth_usage_dec(void);
> > +void attach_dl_bw(struct rq *rq);
> >
> > #ifdef CONFIG_NO_HZ_COMMON
> > enum rq_nohz_flag_bits {
> >
>
> --
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