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Subject: Re: [PATCH] Fix migration of SCHED_DEADLINE tasks
To: Luca Abeni <luca.abeni@unitn.it>, linux-kernel@vger.kernel.org
References: <1444907357-13114-1-git-send-email-luca.abeni@unitn.it>
 <561FD6F3.4090209@arm.com> <5620AF64.4050208@unitn.it>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Wanpeng Li <wanpeng.li@linux.intel.com>
From: Juri Lelli <juri.lelli@arm.com>
Message-ID: <5620BAA5.5010807@arm.com>
Date: Fri, 16 Oct 2015 09:51:49 +0100
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Hi,

On 16/10/15 09:03, Luca Abeni wrote:
> 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.
> 

Thanks!

> 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.
> 

Yeah, it seems we need that fix too.

Best,

- Juri