From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e28smtp06.in.ibm.com (e28smtp06.in.ibm.com [122.248.162.6]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e28smtp06.in.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id C36F22C0090 for ; Thu, 27 Jun 2013 04:25:39 +1000 (EST) Received: from /spool/local by e28smtp06.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 26 Jun 2013 23:48:06 +0530 Received: from d28relay05.in.ibm.com (d28relay05.in.ibm.com [9.184.220.62]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id 2804C3940053 for ; Wed, 26 Jun 2013 23:55:33 +0530 (IST) Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r5QIPUuE27000942 for ; Wed, 26 Jun 2013 23:55:30 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r5QIPVK0032708 for ; Thu, 27 Jun 2013 04:25:33 +1000 Message-ID: <51CB3159.8000509@linux.vnet.ibm.com> Date: Wed, 26 Jun 2013 23:52:17 +0530 From: "Srivatsa S. Bhat" MIME-Version: 1.0 To: Tejun Heo Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to prevent CPU offline 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> In-Reply-To: <20130626152148.GA4405@mtj.dyndns.org> Content-Type: text/plain; charset=ISO-8859-1 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, Steven Rostedt , 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 , 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 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