Re: [PATCH RESEND v10] sched/deadline: support dl task migration during cpu hotplug

From: Wanpeng Li
Date: Tue Mar 17 2015 - 04:11:33 EST


Hi Ingo,
On Tue, Mar 17, 2015 at 09:06:13AM +0100, Ingo Molnar wrote:
>
>* Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx> 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?

Regards,
Wanpeng Li

>
>Thanks,
>
> Ingo
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