From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751579Ab1GSAxQ (ORCPT ); Mon, 18 Jul 2011 20:53:16 -0400 Received: from mga14.intel.com ([143.182.124.37]:4244 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750977Ab1GSAxP (ORCPT ); Mon, 18 Jul 2011 20:53:15 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,225,1309762800"; d="scan'208";a="28721269" Subject: Re: nohz: remove nohz_cpu_mask From: "Alex,Shi" To: "tglx@linutronix.de" Cc: "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "Fu, Michael" , "paulmck@linux.vnet.ibm.com" In-Reply-To: <1310691105.28599.277.camel@debian> References: <1310345225.28599.10.camel@debian> <20110711173047.GL2245@linux.vnet.ibm.com> <1310691105.28599.277.camel@debian> Content-Type: text/plain; charset="UTF-8" Date: Tue, 19 Jul 2011 08:53:20 +0800 Message-ID: <1311036800.27358.26.camel@debian> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thomas: Maybe you omit this thread, So I ping you again. :) What's your opinion of this patch? I will be glad to hear from you for any messages. Regards! Alex On Fri, 2011-07-15 at 08:51 +0800, Alex,Shi wrote: > On Tue, 2011-07-12 at 01:30 +0800, Paul E. McKenney wrote: > > On Mon, Jul 11, 2011 at 08:47:05AM +0800, Alex,Shi wrote: > > > RCU didn't use this global variable now. Currently no user on it. > > > > Indeed. RCU's use of it turned out to be quite buggy. :-( > > > > > Since the ts->do_timer_last is not the real last periodic tick cpu in > > > most of time. I once want to compare the cpu_online_mask and > > > nohz_cpu_mask to get a real one, and than only let that cpu sleep > > > shorter, other cpu will try to sleep KTIME_MAX, that need a extra lock > > > for nohz_cpu_mask. But I checked my all platforms, from NHM-EX server to > > > laptops, all of them are waked up a few times per second. So, the > > > advantage is only in theory. > > > > > > Since no clear usage of this variable, why not remove it? That can save > > > a cache-line in all cpus and reduce atomic sync contention. > > > > Works for me! > > > > Reviewed-by: Paul E. McKenney > > > > Thomas, would you like to give some comments of this? > > Best regards! > Alex