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Date: Sun, 30 Aug 2015 19:25:08 +0800
From: Wanpeng Li <wanpeng.li@...mail.com>
To: Juri Lelli <juri.lelli@....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
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? ;-)
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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