From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to prevent CPU offline Date: Wed, 26 Jun 2013 07:34:24 -0700 Message-ID: <20130626143424.GN3828@linux.vnet.ibm.com> References: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> <20130625202755.16593.67819.stgit@srivatsabhat.in.ibm.com> <20130625220026.GG3828@linux.vnet.ibm.com> <51CAF624.6060004@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Srivatsa S. Bhat" , peterz@infradead.org, fweisbec@gmail.com, linux-kernel@vger.kernel.org, walken@google.com, mingo@kernel.org, linux-arch@vger.kernel.org, vincent.guittot@linaro.org, xiaoguangrong@linux.vnet.ibm.com, wangyun@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, rusty@rustcorp.com.au, rostedt@goodmis.org, namhyung@kernel.org, tglx@linutronix.de, laijs@cn.fujitsu.com, zhong@linux.vnet.ibm.com, netdev@vger.kernel.org, oleg@redhat.com, sbw@mit.edu, tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org To: David Laight Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Jun 26, 2013 at 03:29:40PM +0100, David Laight wrote: > > Once stop_machine() is gone from the CPU offline path, we won't be able > > to depend on disabling preemption to prevent CPUs from going offline > > from under us. > > Could you use an rcu-like sequence so that disabling pre-emption > would be enough? > > Something like rebuilding the cpu list, then forcing yourself > to run on all the cpu. > > That would be far less intrusive. It would also increase the latency of CPU-hotunplug operations. Thanx, Paul