linux-kernel - Re:[PATCH] sched/rt: Fix pull_rt_task() skips not overloaded rqs

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Message-Id: <281621375376081@web1e.yandex.ru>
Date:	Thu, 01 Aug 2013 20:54:41 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re:[PATCH] sched/rt: Fix pull_rt_task() skips not overloaded rqs

This is bad patch. Sorry for the noise.


> The main patch profit is deletion of the following check
> at the beginning of pull_rt_task():
> 
> if (likely(!rt_overloaded(this_rq)))
> return 0;
> 
> This check makes pull_rt_task() nearly useless, because
> it kills all cases like "last RT task has just gone away".
> The check is better suitable for push_rt_task().
> 
> So, kill the check, now unusable rt_overloaded() and rto_count.
> 
> Move root_domain's refcount to the bottom of the structure
> to keep its fields aligned.
> 
> Signed-off-by: Kirill Tkhai <tkhai@...dex.ru>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> ---
> kernel/sched/rt.c | 19 -------------------
> kernel/sched/sched.h | 3 +--
> 2 files changed, 1 insertions(+), 21 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 01970c8..cf297a7 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -229,26 +229,12 @@ int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
> 
> #ifdef CONFIG_SMP
> 
> -static inline int rt_overloaded(struct rq *rq)
> -{
> - return atomic_read(&rq->rd->rto_count);
> -}
> -
> static inline void rt_set_overload(struct rq *rq)
> {
> if (!rq->online)
> return;
> 
> cpumask_set_cpu(rq->cpu, rq->rd->rto_mask);
> - /*
> - * Make sure the mask is visible before we set
> - * the overload count. That is checked to determine
> - * if we should look at the mask. It would be a shame
> - * if we looked at the mask, but the mask was not
> - * updated yet.
> - */
> - wmb();
> - atomic_inc(&rq->rd->rto_count);
> }
> 
> static inline void rt_clear_overload(struct rq *rq)
> @@ -256,8 +242,6 @@ static inline void rt_clear_overload(struct rq *rq)
> if (!rq->online)
> return;
> 
> - /* the order here really doesn't matter */
> - atomic_dec(&rq->rd->rto_count);
> cpumask_clear_cpu(rq->cpu, rq->rd->rto_mask);
> }
> 
> @@ -1627,9 +1611,6 @@ static int pull_rt_task(struct rq *this_rq)
> struct task_struct *p;
> struct rq *src_rq;
> 
> - if (likely(!rt_overloaded(this_rq)))
> - return 0;
> -
> for_each_cpu(cpu, this_rq->rd->rto_mask) {
> if (this_cpu == cpu)
> continue;
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 4c1cb80..1f36afb 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -374,8 +374,6 @@ struct rt_rq {
> *
> */
> struct root_domain {
> - atomic_t refcount;
> - atomic_t rto_count;
> struct rcu_head rcu;
> cpumask_var_t span;
> cpumask_var_t online;
> @@ -386,6 +384,7 @@ struct root_domain {
> */
> cpumask_var_t rto_mask;
> struct cpupri cpupri;
> + atomic_t refcount;
> };
> 
> extern struct root_domain def_root_domain;
> --
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