From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932684Ab1GOAv6 (ORCPT ); Thu, 14 Jul 2011 20:51:58 -0400 Received: from mga09.intel.com ([134.134.136.24]:17396 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932409Ab1GOAv5 (ORCPT ); Thu, 14 Jul 2011 20:51:57 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,532,1304319600"; d="scan'208";a="27867219" Subject: Re: nohz: remove nohz_cpu_mask From: "Alex,Shi" To: "paulmck@linux.vnet.ibm.com" Cc: "tglx@linutronix.de" , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "Fu, Michael" In-Reply-To: <20110711173047.GL2245@linux.vnet.ibm.com> References: <1310345225.28599.10.camel@debian> <20110711173047.GL2245@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 15 Jul 2011 08:51:45 +0800 Message-ID: <1310691105.28599.277.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 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