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Date: Tue, 17 Mar 2015 15:59:45 +0800
From: Wanpeng Li <wanpeng.li@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Wanpeng Li <wanpeng.li@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@arm.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND v10] sched/deadline: support dl task migration
 during cpu hotplug
Message-ID: <20150317075945.GA5646@kernel>
Reply-To: Wanpeng Li <wanpeng.li@linux.intel.com>
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On Tue, Mar 17, 2015 at 09:13:02AM +0100, Ingo Molnar wrote:
>
>* Wanpeng Li <wanpeng.li@linux.intel.com> wrote:
>
>> Hi Ingo,
>> On Tue, Mar 17, 2015 at 09:06:13AM +0100, Ingo Molnar wrote:
>> >
>> >* Wanpeng Li <wanpeng.li@linux.intel.com> wrote:
>> >
>> >> Hi Ingo,
>> >> On Mon, Mar 16, 2015 at 04:01:02PM +0100, Ingo Molnar wrote:
>> >> >> +
>> >> >> +			/*
>> >> >> +			 * If cannot preempt any rq, fallback to pick any
>> >> >> +			 * online cpu.
>> >> >
>> >> >s/If cannot/If we cannot
>> >> >s/fallback/fall back
>> >> 
>> >> Will do.
>> >> 
>> >> >
>> >> >> +			 */
>> >> >> +			fallback = true;
>> >> >> +			cpu = cpumask_any_and(cpu_active_mask,
>> >> >> +						tsk_cpus_allowed(p));
>> >> >
>> >> >shouldn't be on separate lines - but this is also a sign that the guts 
>> >> 
>> >> Otherwise there is a "WARNING: line over 80 characters".
>> >
>> >Yes, but did your reaction to that tool's warning improve the code? I 
>> >don't think so. If do what I suggested and reduce indentation a bit, 
>> >you'll fix the warning _and_ improve the code. Win-win.
>> 
>> Cool, will do.
>> 
>> >
>> >> > of this new code should be in a helper function, not inside 
>> >> > several layers of branches.
>> >> 
>> >> Do you mean the whole patch should be in a helper function?
>> >
>> >Probably.
>> 
>> Will do.
>> 
>> >
>> >> >> +			if (cpu >= nr_cpu_ids) {
>> >> >> +				if (dl_bandwidth_enabled()) {
>> >> >> +					/*
>> >> >> +					 * Fail to find any suitable cpu.
>> >> >> +					 * The task will never come back!
>> >> >> +					 */
>> >> >> +					WARN_ON(1);
>> >> >
>> >> > Can this condition happen to users with a non-buggy kernel?
>> >> 
>> >> What do you prefer? ;-)
>> >
>> >That was a yes/no question: can this condition trigger on correctly 
>> >working kernels?
>> 
>> How about add unlikely() here? 
>
>Please answer my question: can this condition trigger on correctly 
>working kernels? I think so, but maybe I'm wrong?

I didn't see it happen, I add this by Juri's suggestion, maybe he can 
explain more.

Ping Juri, ;-)

Regards,
Wanpeng Li

>
>Yes/no.
>
>Thanks,
>
>	Ingo