From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752007Ab2LTSQ5 (ORCPT ); Thu, 20 Dec 2012 13:16:57 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:52297 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274Ab2LTSQv (ORCPT ); Thu, 20 Dec 2012 13:16:51 -0500 Message-ID: <50D3560E.7080802@linaro.org> Date: Thu, 20 Dec 2012 19:16:46 +0100 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: "Rafael J. Wysocki" CC: Sivaram Nair , Russ Anderson , Peter De Schrijver , "akpm@linux-foundation.org" , "shuox.liu@intel.com" , "yanmin_zhang@intel.com" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [regression] cpuidle_get_cpu_driver livelocks idle system References: <20121217193612.GA28600@sgi.com> <50CF95AD.8030406@linaro.org> <2092099.bR8HA2X8Pe@vostro.rjw.lan> In-Reply-To: <2092099.bR8HA2X8Pe@vostro.rjw.lan> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/18/2012 12:33 AM, Rafael J. Wysocki wrote: > On Monday, December 17, 2012 10:59:09 PM Daniel Lezcano wrote: >> On 12/17/2012 08:36 PM, Russ Anderson wrote: >>> The 3.7 kernel grinds to a halt on boot of a system with >>> 2048 cpus. NMI showed most of the cpus in >>> _raw_spin_lock in cpuidle_get_cpu_driver(). (backtrace below) >>> >>> A quick look at cpuidle_get_cpu_driver() shows the hot lock. >>> >>> In drivers/cpuidle/driver.c: >>> -------------------------------------------------------- >>> /** >>> * cpuidle_get_cpu_driver - return the driver tied with a cpu >>> */ >>> struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev) >>> { >>> struct cpuidle_driver *drv; >>> >>> if (!dev) >>> return NULL; >>> >>> spin_lock(&cpuidle_driver_lock); >>> drv = __cpuidle_get_cpu_driver(dev->cpu); >>> spin_unlock(&cpuidle_driver_lock); >>> >>> return drv; >>> } >>> -------------------------------------------------------- >> >> Hi Russ, >> >> thanks for investigating the problem. You are right, there is a >> bottleneck here. >> >> Regarding how is used the cpuidle code, I think it is safe to remove the >> locks. > > OK, a patch would be appreciated. :-) > > If you prepare one, please explain in the changelog why it is safe to drop the > locks. Ok, sure. I have some troubles with my x86 hardware, so it could take a couple of days before I can send a fix a bit tested. >>> This change was added in on Nov 14th, 2012. >>> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commit;h=bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92 >>> >>> The patch says it adds support for cpus with different characteristics, >>> but adds a big global lock. The comment claims "no impact for the other >>> platforms if the option is disabled", which leads me to believe the >>> spin_lock was added inadvertently. CPU_IDLE_MULTIPLE_DRIVERS is off >>> in my config file. >>> >>> linux$ grep CPU_IDLE_MULTIPLE_DRIVERS .config >>> # CONFIG_CPU_IDLE_MULTIPLE_DRIVERS is not set >>> >>> As more cpus become idle, more cpus fight over the lock until >>> the system livelocks on the crushing weight of idle. >>> >>> The fix may be to move the spin_lock into __cpuidle_get_cpu_driver, >>> which has different versions for CONFIG_CPU_IDLE_MULTIPLE_DRIVERS, >>> to avoid impacting the disabled case, or get rid of the spin_lock >>> all together. >>> >>> >>> -------------------------------------------------------- >>> == UV NMI process trace cpu 12: == >>> CPU 12 >>> Pid: 0, comm: swapper/12 Tainted: G O 3.7.0.rja-sgi+ #38 >>> RIP: 0010:[] [] _raw_spin_lock+0x25/0x30 >>> [...] >>> Call Trace: >>> [] cpuidle_get_cpu_driver+0x1c/0x30 >>> [] cpuidle_idle_call+0x7d/0x1b0 >>> [] cpu_idle+0xdd/0x130 >>> [] start_secondary+0xc6/0xcc >>> -------------------------------------------------------- >>> >> >> >> -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog