From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hrndva-omtalb.mail.rr.com (hrndva-omtalb.mail.rr.com [71.74.56.122]) by ozlabs.org (Postfix) with ESMTP id 1C2BC2C008A for ; Thu, 27 Jun 2013 01:33:47 +1000 (EST) Message-ID: <1372260823.18733.263.camel@gandalf.local.home> Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to prevent CPU offline From: Steven Rostedt To: Tejun Heo Date: Wed, 26 Jun 2013 11:33:43 -0400 In-Reply-To: <20130626152148.GA4405@mtj.dyndns.org> 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> <20130626143424.GN3828@linux.vnet.ibm.com> <1372258271.18733.256.camel@gandalf.local.home> <20130626152148.GA4405@mtj.dyndns.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: peterz@infradead.org, fweisbec@gmail.com, oleg@redhat.com, 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, paulmck@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, rusty@rustcorp.com.au, namhyung@kernel.org, tglx@linutronix.de, laijs@cn.fujitsu.com, zhong@linux.vnet.ibm.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, sbw@mit.edu, David Laight , "Srivatsa S. Bhat" , akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2013-06-26 at 08:21 -0700, Tejun Heo wrote: > On Wed, Jun 26, 2013 at 10:51:11AM -0400, Steven Rostedt wrote: > > > It would also increase the latency of CPU-hotunplug operations. > > > > Is that a big deal? > > I thought that was the whole deal with this patchset - making cpu > hotunplugs lighter and faster mostly for powersaving. That said, just > removing stop_machine call would be a pretty good deal and I don't > know how meaningful reducing CPU hotunplug latency is. Srivatsa? I thought the whole deal with this patchset was to remove stop_machine from CPU hotplug. Why halt all CPUs just to remove one? stomp_machine() is extremely intrusive for the entire system, where as one CPU making sure all CPUs schedule isn't very intrusive at all. I didn't think the idea of this patch set was to make CPU hotplug faster, just less intrusive to the system. -- Steve