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

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Message-ID: <20140213110615.GA17359@in.ibm.com>
Date:	Thu, 13 Feb 2014 16:36:15 +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, oleg@...hat.com, rusty@...tcorp.com.au,
	peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, mingo@...nel.org,
	paulmck@...ux.vnet.ibm.com, tj@...nel.org, walken@...gle.com,
	ego@...ux.vnet.ibm.com, linux@....linux.org.uk,
	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 Mon, Feb 10, 2014 at 06:26:20PM -0700, Toshi Kani wrote:
> 
> get/put_online_cpus() is a reader-lock and concurrent executions are
> allowed among the readers.  They won't be serialized until a cpu
> online/offline operation begins.  By replacing this lock with
> cpu_maps_update_begin/done(), we now serialize all readers.

We're not serializing all the readers, just the ones which want to
register/unregister their cpu-hotplug notifiers. This is a one-off
event which typically happens during a module_init() or a
module_exit() time. So this patchset does not replace
get/put_online_cpus() if that is the concern!

--
Thanks and Regards
gautham.
 


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