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Date: Tue, 01 Sep 2015 10:49:37 +0100
From: Juri Lelli <juri.lelli@....com>
To: Wanpeng Li <wanpeng.li@...mail.com>,
Wanpeng Li <kernellwp@...il.com>,
Peter Zijlstra <peterz@...radead.org>
CC: Ingo Molnar <mingo@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/deadline: fix dl bandwidth of root domain overflow
after dl task dead
Hi,
On 30/08/15 12:25, Wanpeng Li wrote:
> On 8/10/15 10:10 PM, Juri Lelli wrote:
>> 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.
>
> Ping Peter, Juri, any detail ideas to help me post another version of my
> patch? ;-)
>
Let me see if I'm able to post my version of the fix before
end of this week ;).
Thanks!
- Juri
> Regards,
> Wanpeng Li
>
>>
>> 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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