linux-kernel - Re: [PATCH] Avoid mask based num_possible_cpus and num_online

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Message-ID: <CABeCy1aWv1DmqrkbBJ=JmAK7UkSLH+yPK-EG+58_573yG3jsHg@mail.gmail.com>
Date:	Fri, 20 Jan 2012 15:55:36 -0800
From:	Venki Pallipadi <venki@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Travis <travis@....com>,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus

On Fri, Jan 20, 2012 at 3:45 PM, KOSAKI Motohiro
<kosaki.motohiro@...il.com> wrote:
>>>> +int nr_online_cpus __read_mostly;
>>>> +EXPORT_SYMBOL(nr_online_cpus);
>>>> +
>>>>  void set_cpu_possible(unsigned int cpu, bool possible)
>>>>  {
>>>>       if (possible)
>>>
>>>
>>> Did you forget to add:
>>>
>>>        nr_possible_cpus = cpumask_weight(cpu_possible_mask);
>>>
>>> inside set_cpu_possible() ?
>>
>> No. That was intentional as I have that coupled with nr_cpu_ids and
>> set once after all the bits are set in setup_nr_cpu_ids() instead of
>> doing for each bit set.
>
> But, Srivatsa's way seems more safer, no? Is there any advantage to make couple
> with nr_cpu_ids?

I think it is a tradeoff between safer and cleaner :). infact, that's
how I had coded the patch first. But, then I changed it to be in sync
with nr_cpu_ids as it seemed a bit cleaner (and also to make sure 2048
CPU guys won't come after me for doing the mask calculation 2048 times
during the boot).
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