From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to prevent CPU offline Date: Wed, 26 Jun 2013 23:52:17 +0530 Message-ID: <51CB3159.8000509@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> <20130626143424.GN3828@linux.vnet.ibm.com> <1372258271.18733.256.camel@gandalf.local.home> <20130626152148.GA4405@mtj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Steven Rostedt , paulmck@linux.vnet.ibm.com, David Laight , 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, 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, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org To: Tejun Heo Return-path: In-Reply-To: <20130626152148.GA4405@mtj.dyndns.org> Sender: linux-pm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 06/26/2013 08:51 PM, 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? > Keeping the hotunplug latency is important for suspend/resume, where we take all non-boot CPUs in a loop. That's an interesting use-case where intrusiveness doesn't matter much, but latency does. So yes, making CPU hotplug faster is also one of the goals of this patchset. Regards, Srivatsa S. Bhat