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

From: Wanpeng Li
Date: Tue Mar 17 2015 - 04:17:58 EST


On Tue, Mar 17, 2015 at 09:13:02AM +0100, Ingo Molnar wrote:
>
>* Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx> wrote:
>
>> 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?
>
>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
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