linux-kernel - Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callback registration functions

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Message-ID: <20140211171805.GA3932@in.ibm.com>
Date:	Tue, 11 Feb 2014 22:48:05 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"tj@...nel.org" <tj@...nel.org>,
	"walken@...gle.com" <walken@...gle.com>,
	"ego@...ux.vnet.ibm.com" <ego@...ux.vnet.ibm.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callback
 registration functions

On Tue, Feb 11, 2014 at 09:33:56AM -0700, Toshi Kani wrote:
> 
> I agree that introducing a reader-writer semaphore allows concurrent
> executions.  Adding yet another hotplug lock is a bit unfortunate,
> though.
> 

I agree with this last part. We already have enough locks for
cpu-hotplug. Another one sounds one too many!!


> This may be a dumb question, but can't we simply do this way?
> 
>         get_online_cpus();
> 
>         for_each_online_cpu(cpu)
>                 init_cpu(cpu);
> 
>         put_online_cpus();
>
      -------- Someone chooses to hotplug a cpu here ------
      -------- But this subsystem might miss out on knowing
               about it since it hasn't registered its
               notifier yet! 

>         register_cpu_notifier(&foobar_cpu_notifier);
> 
> Thanks,
> -Toshi
> 

--
Thanks and Regards
gautham.

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