linux-kernel - Re: [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context

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Message-ID: <20121209211338.GA8090@redhat.com>
Date:	Sun, 9 Dec 2012 22:13:38 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	vincent.guittot@...aro.org, tj@...nel.org, sbw@....edu,
	amit.kucheria@...aro.org, rostedt@...dmis.org, rjw@...k.pl,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPU
	offline from atomic context

Damn, sorry for noise. I missed this part...

On 12/10, Srivatsa S. Bhat wrote:
>
> On 12/10/2012 12:44 AM, Oleg Nesterov wrote:
> > the latency. And I guess something like kick_all_cpus_sync() is "too heavy".
>
> I hadn't considered that. Thinking of it, I don't think it would help us..
> It won't get rid of the currently running preempt_disable() sections no?

Sure. But (again, this is only my feeling so far) given that get_online_cpus_atomic()
does cli/sti, this can help to implement ensure-the-readers-must-see-the-pending-writer.
IOW this might help to implement sync-with-readers.

Oleg.

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