linux-kernel - Re: [PATCH] Fix migration of SCHED

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Date:	Fri, 16 Oct 2015 10:03:48 +0200
From:	Luca Abeni <luca.abeni@...tn.it>
To:	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH] Fix migration of SCHED_DEADLINE tasks

On 10/15/2015 06:40 PM, Juri Lelli wrote:
> On 15/10/15 12:09, Luca Abeni wrote:
>> Commit 9d5142624256 ("sched/deadline: Reduce rq lock contention by
>> eliminating locking of non-feasible target") broke select_task_rq_dl()
[...]
>> -				dl_time_before(p->dl.deadline,
>> -					cpu_rq(target)->dl.earliest_dl.curr))
>> +				(dl_time_before(p->dl.deadline,
>> +					cpu_rq(target)->dl.earliest_dl.curr) ||
>> +				(cpu_rq(target)->dl.earliest_dl.curr == 0)))
>
> Can't we actually use dl.dl_nr_running here and below, so
> that we won't incur any wraparound problem?
Ok, I tested the patch with dl.dl_nr_running and if works for me...

I am going to send the updated patch in few minutes.

BTW, should we also use "dl_rq->dl_nr_running == 0" instead of
"dl_rq->earliest_dl.curr == 0" in inc_dl_deadline(), and remove the
comment from init_dl_rq()? If you think it is a good idea, I'll test this
additional change and send a patch in next week.



				Thanks,
					Luca
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