Return-Path: <linux-kernel-owner+w=401wt.eu-S1762080AbXJXSW6@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1762080AbXJXSW6 (ORCPT <rfc822;w@1wt.eu>);
	Wed, 24 Oct 2007 14:22:58 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756385AbXJXSWt
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Wed, 24 Oct 2007 14:22:49 -0400
Received: from E23SMTP04.au.ibm.com ([202.81.18.173]:33975 "EHLO
	e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1756241AbXJXSWr (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 24 Oct 2007 14:22:47 -0400
Date: Wed, 24 Oct 2007 23:52:10 +0530
From: Gautham R Shenoy <ego@in.ibm.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Christoph Lameter <clameter@sgi.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Rusty Russel <rusty@rustcorp.com.au>,
       Srivatsa Vaddagiri <vatsa@in.ibm.com>,
       Dipankar Sarma <dipankar@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       Paul E McKenney <paulmck@us.ibm.com>,
       Richard Gooch <rgooch@atnf.csiro.au>,
       Tigran Aivazian <tigran@aivazian.fs.co.uk>,
       Shoahua Li <shaohua.li@linux.com>, Ralf Baechle <ralf@linux-mips.org>,
       Heiko Carstens <heiko.carstens@de.ibm.com>,
       Nathan Lynch <ntl@pobox.com>, David Miller <davem@davemloft.net>,
       Paul Jackson <pj@sgi.com>, Josh Triplett <josh@freedesktop.org>,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       Akinobu Mita <akinobu.mita@gmail.com>
Subject: Re: [RFC PATCH 0/5] Refcount based Cpu Hotplug. V2
Message-ID: <20071024182210.GA10884@in.ibm.com>
Reply-To: ego@in.ibm.com
References: <20071024052931.GA22722@in.ibm.com> <Pine.LNX.4.64.0710241001160.26202@schroedinger.engr.sgi.com> <20071024180034.GB8663@in.ibm.com> <20071024181754.GC345@tv-sign.ru>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20071024181754.GC345@tv-sign.ru>
User-Agent: Mutt/1.5.15+20070412 (2007-04-11)
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1439
Lines: 42

On Wed, Oct 24, 2007 at 10:17:54PM +0400, Oleg Nesterov wrote:
> On 10/24, Gautham R Shenoy wrote:
> >
> > On Wed, Oct 24, 2007 at 10:04:41AM -0700, Christoph Lameter wrote:
> > > On Wed, 24 Oct 2007, Gautham R Shenoy wrote:
> > > 
> > > > This is the version 2 of the refcount based cpu-hotplug "locking" 
> > > > implementation. 
> > > 
> > > Uggh. This introduces a global lock that has to be taken always when 
> > > scanning over cpus? 
> > 
> > Well, no! we take the global lock only while bumping up the refcount. 
> > We don't hold the lock while scanning over the cpus. And this is
> > definitely an improvement over the lock_cpu_hotplug() global mutex
> > we have now.
> 
> Just to be sure I didn't miss something... preempt_disable() still works,
> yes?

Yes it does. But it doesn't prevent onlining of new cpus. 
I am checking if __cpu_up() can also be called safely using
stop_machine_run() so that we can use preempt_disable() for safe atomic
access of the cpu_online_map.

> 
> Oleg.
> 

Thanks and Regards
gautham.
-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/