From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755516AbaGCFsp (ORCPT ); Thu, 3 Jul 2014 01:48:45 -0400 Received: from mail-we0-f175.google.com ([74.125.82.175]:54243 "EHLO mail-we0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbaGCFso (ORCPT ); Thu, 3 Jul 2014 01:48:44 -0400 Message-ID: <1404366520.5137.90.camel@marge.simpson.net> Subject: Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread wakeups From: Mike Galbraith To: paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, riel@redhat.com, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu Date: Thu, 03 Jul 2014 07:48:40 +0200 In-Reply-To: <20140703052124.GB4603@linux.vnet.ibm.com> References: <20140627142038.GA22942@linux.vnet.ibm.com> <20140702123412.GD19379@twins.programming.kicks-ass.net> <20140702153915.GQ4603@linux.vnet.ibm.com> <20140702160412.GO19379@twins.programming.kicks-ass.net> <20140702170838.GS4603@linux.vnet.ibm.com> <1404358279.5137.63.camel@marge.simpson.net> <20140703052124.GB4603@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2014-07-02 at 22:21 -0700, Paul E. McKenney wrote: > On Thu, Jul 03, 2014 at 05:31:19AM +0200, Mike Galbraith wrote: > > NO_HZ_FULL is a property of a set of CPUs. isolcpus is supposed to go > > away as being a redundant interface to manage a single property of a set > > of CPUs, but it's perfectly fine for NO_HZ_FULL to add an interface to > > manage a single property of a set of CPUs. What am I missing? > > Well, for now, it can only be specified at build time or at boot time. > In theory, it is possible to change a CPU from being callback-offloaded > to not at runtime, but there would need to be an extremely good reason > for adding that level of complexity. Lots of "fun" races in there... Yeah, understood. (still it's a NO_HZ_FULL wart though IMHO, would be prettier and more usable if it eventually became unified with cpuset and learned how to tap-dance properly;) -Mike