From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030184Ab2LEU5z (ORCPT ); Wed, 5 Dec 2012 15:57:55 -0500 Received: from mail-da0-f46.google.com ([209.85.210.46]:49218 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964817Ab2LEU5v (ORCPT ); Wed, 5 Dec 2012 15:57:51 -0500 Date: Wed, 5 Dec 2012 12:57:44 -0800 From: Tejun Heo To: "Srivatsa S. Bhat" Cc: tglx@linutronix.de, peterz@infradead.org, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, vincent.guittot@linaro.org, oleg@redhat.com, sbw@mit.edu, amit.kucheria@linaro.org, rostedt@goodmis.org, rjw@sisk.pl, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 02/10] CPU hotplug: Provide APIs for "full" atomic readers to prevent CPU offline Message-ID: <20121205205744.GB27465@mtj.dyndns.org> References: <20121205184041.3750.64945.stgit@srivatsabhat.in.ibm.com> <20121205184313.3750.17752.stgit@srivatsabhat.in.ibm.com> <50BF99FA.8060109@linux.vnet.ibm.com> <50BFAF27.9060203@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50BFAF27.9060203@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Dec 06, 2012 at 02:01:35AM +0530, Srivatsa S. Bhat wrote: > Yes, that _sounds_ sufficient, but IMHO it won't be, in practice. The > *number* of call-sites that you need to convert from preempt_disable/enable > to get/put_online_cpus_atomic() won't be too many, however the *frequency* > of usage of those call-sites can potentially be very high. I don't think that will be the case and, even if it is, doing it this way would make it difficult to tell. The right thing to do is replacing stop_machine with finer grained percpu locking first. Refining it further should happen iff that isn't enough and there isn't an simpler solution. So, let's please do the simple conversion first. Thanks. -- tejun