From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp02.au.ibm.com (e23smtp02.au.ibm.com [202.81.31.144]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e23smtp02.au.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id A5DD82C008D for ; Tue, 8 Jan 2013 17:57:47 +1100 (EST) Received: from /spool/local by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 8 Jan 2013 16:52:49 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id AD4652CE804D for ; Tue, 8 Jan 2013 17:57:37 +1100 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r086k9a558785846 for ; Tue, 8 Jan 2013 17:46:09 +1100 Received: from d23av03.au.ibm.com (loopback [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r086vYQm022837 for ; Tue, 8 Jan 2013 17:57:36 +1100 Message-ID: <50EBC2F9.70303@linux.vnet.ibm.com> Date: Tue, 08 Jan 2013 12:25:53 +0530 From: "Srivatsa S. Bhat" MIME-Version: 1.0 To: Russell King - ARM Linux Subject: Re: [PATCH 1/2] cpuhotplug/nohz: Remove offline cpus from nohz-idle state References: <1357268318-7993-1-git-send-email-vatsa@codeaurora.org> <20130105103627.GU2631@n2100.arm.linux.org.uk> In-Reply-To: <20130105103627.GU2631@n2100.arm.linux.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-mips@linux-mips.org, linux-sh@vger.kernel.org, Peter Zijlstra , Srivatsa Vaddagiri , mhocko@suse.cz, "H. Peter Anvin" , sparclinux@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, Ingo Molnar , "Paul E. McKenney" , Mike Frysinger , Nikunj A Dadhania , linux-arm-msm@vger.kernel.org, "rusty@rustcorp.com.au" , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Stephen Boyd , linux-kernel@vger.kernel.org, Ralf Baechle , Paul Mundt , Martin Schwidefsky , uclinux-dist-devel@blackfin.uclinux.org, linuxppc-dev@lists.ozlabs.org, "David S. Miller" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 01/05/2013 04:06 PM, Russell King - ARM Linux wrote: > On Thu, Jan 03, 2013 at 06:58:38PM -0800, Srivatsa Vaddagiri wrote: >> I also think that the >> wait_for_completion() based wait in ARM's __cpu_die() can be replaced with a >> busy-loop based one, as the wait there in general should be terminated within >> few cycles. > > Why open-code this stuff when we have infrastructure already in the kernel > for waiting for stuff to happen? I chose to use the standard infrastructure > because its better tested, and avoids having to think about whether we need > CPU barriers and such like to ensure that updates are seen in a timely > manner. > > My stance on a lot of this idle/cpu dying code is that much of it can > probably be cleaned up and merged into a single common implementation - > in which case the use of standard infrastructure for things like waiting > for other CPUs do stuff is even more justified. On similar lines, Nikunj (in CC) and I had posted a patchset sometime ago to consolidate some of the CPU hotplug related code in the various architectures into a common standard implementation [1]. However, we ended up hitting a problem with Xen, because its existing code was unlike the other arch/ pieces [2]. At that time, we decided that we will first make the CPU online and offline paths symmetric in the generic code and then provide a common implementation of the duplicated bits in arch/, for the new CPU hotplug model [3]. I guess we should probably revisit it sometime, consolidating the code in incremental steps if not all at a time... -- [1]. http://lwn.net/Articles/500185/ [2]. http://thread.gmane.org/gmane.linux.kernel.cross-arch/14342/focus=14430 [3]. http://thread.gmane.org/gmane.linux.kernel.cross-arch/14342/focus=15567 Regards, Srivatsa S. Bhat