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

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Message-ID: <20150407225755.GA9966@kernel>
Date:	Wed, 8 Apr 2015 06:57:56 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Juri Lelli <juri.lelli@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH 3/7] sched/deadline: reduce rq lock contention by
 eliminating locking of non-feasible target

Hi Juri,
On Tue, Apr 07, 2015 at 02:48:12PM +0100, Juri Lelli wrote:
>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?
>

Good point, will do. Great thanks for your review. :)

Regards,
Wanpeng Li 

>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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