linux-kernel - Re: [PATCH 3/7] sched/deadline: reduce rq lock contention by eliminating locking of non-feasible target

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Date:	Tue, 07 Apr 2015 14:48:12 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] sched/deadline: reduce rq lock contention by eliminating
 locking of non-feasible target

Hi,

On 06/04/2015 09:53, Wanpeng Li wrote:
> This patch adds check that prevents futile attempts to move dl tasks to
> a CPU with active tasks of equal or earlier deadline. The same behavior as
> commit 80e3d87b2c55 ("sched/rt: Reduce rq lock contention by eliminating
> locking of non-feasible target") for rt class.
> 

This commit introduced also this kind of check in find_lock_lowest_rq().
Don't we need something like this in find_lock_later_rq() as well?

Thanks,

- Juri

> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  kernel/sched/deadline.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 3bd3158..b8b9355 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1012,7 +1012,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
>  	    (p->nr_cpus_allowed > 1)) {
>  		int target = find_later_rq(p);
>  
> -		if (target != -1)
> +		if (target != -1 &&
> +			dl_time_before(p->dl.deadline,
> +				cpu_rq(target)->dl.earliest_dl.curr))
>  			cpu = target;
>  	}
>  	rcu_read_unlock();
> 

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