From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759036Ab2LIVNj (ORCPT ); Sun, 9 Dec 2012 16:13:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44242 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753209Ab2LIVNh (ORCPT ); Sun, 9 Dec 2012 16:13:37 -0500 Date: Sun, 9 Dec 2012 22:13:38 +0100 From: Oleg Nesterov 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, tj@kernel.org, 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 v3 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Message-ID: <20121209211338.GA8090@redhat.com> References: <20121207173702.27305.1486.stgit@srivatsabhat.in.ibm.com> <20121207173759.27305.84316.stgit@srivatsabhat.in.ibm.com> <20121209191437.GA2816@redhat.com> <50C4EB79.5050203@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50C4EB79.5050203@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.