Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758461AbZJEDdm (ORCPT ); Sun, 4 Oct 2009 23:33:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758424AbZJEDdl (ORCPT ); Sun, 4 Oct 2009 23:33:41 -0400 Received: from e28smtp07.in.ibm.com ([59.145.155.7]:50175 "EHLO e28smtp07.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758346AbZJEDdl (ORCPT ); Sun, 4 Oct 2009 23:33:41 -0400 Date: Mon, 5 Oct 2009 09:02:56 +0530 From: Balbir Singh To: Len Brown Cc: Linus Torvalds , Andrew Morton , Linux Kernel Mailing List , linux-acpi@vger.kernel.org, Peter Zijlstra , Shaohua Li , Vaidyanathan Srinivasan Subject: Re: [git pull request] ACPI Processor Aggregator Driver for 2.6.32-rc1 Message-ID: <20091005033256.GA26592@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2012 Lines: 48 * Len Brown [2009-10-03 01:56:32]: > This driver does not use the kernel's CPU hot-plug mechanism > because after the transient emergency is over, the system must > be returned to its normal state, and hotplug would permanently > break both cpusets and binding. > Why does hotplug break cpusets and binding? > So to force idle, the driver creates a power saving thread. > The scheduler will migrate the thread to the preferred CPU. > The thread has max priority and has SCHED_RR policy, > so it can occupy one CPU. To save power, the thread will > invoke the deep C-state entry instructions. > > To avoid starvation, the thread will sleep 5% of the time > time for every second (current RT scheduler has threshold > to avoid starvation, but if other CPUs are idle, > the CPU can borrow CPU timer from other, > which makes the mechanism not work here) > > Vaidyanathan Srinivasan has proposed scheduler enhancements > to allow injecting idle time into the system. This driver doesn't > depend on those enhancements, but could cut over to them > when they are available. > > Peter Z. does not favor upstreaming this driver until > the those scheduler enhancements are in place. However, > we favor upstreaming this driver now because it is useful > now, and can be enhanced over time. > > Signed-off-by: Shaohua Li > NACKed-by: Peter Zijlstra > Cc: Vaidyanathan Srinivasan > Signed-off-by: Len Brown This is a first a patch with a NACKed-by, could we please have more discussion on the proposed design. -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/