Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752641AbbFYPax (ORCPT ); Thu, 25 Jun 2015 11:30:53 -0400 Received: from foss.arm.com ([217.140.101.70]:57498 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751469AbbFYPaf (ORCPT ); Thu, 25 Jun 2015 11:30:35 -0400 Message-ID: <558C1E97.4020206@arm.com> Date: Thu, 25 Jun 2015 16:30:31 +0100 From: Sudeep Holla User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Thomas Gleixner CC: Sudeep Holla , "linux-kernel@vger.kernel.org" , Suzuki Poulose , Lorenzo Pieralisi , Catalin Marinas , "Rafael J. Wysocki" , Preeti U Murthy Subject: Re: [PATCH] clockevents: return error from tick_broadcast_oneshot_control if !GENERIC_CLOCKEVENTS_BROADCAST References: <1435228065-2428-1-git-send-email-sudeep.holla@arm.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2008 Lines: 61 On 25/06/15 14:55, Thomas Gleixner wrote: > On Thu, 25 Jun 2015, Sudeep Holla wrote: > >> tick_broadcast_enter returns 0 when CPU can switch to broadcast >> timer and non-zero otherwise. However when GENERIC_CLOCKEVENTS_BROADCAST >> and TICK_ONESHOT are disabled, tick_broadcast_oneshot_control returns 0 >> which indicates to the CPUIdle framework that the CPU can enter deeper >> idle states even when the CPU local timer will be shutdown. If the >> target state needs broadcast but not broadcast timer is available, then >> the CPU can not resume back from that idle state. >> >> This patch returns error when there's no broadcast timer support >> available so that CPUIdle framework prevents the CPU from entering any >> idle states losing the local timer. > > That's wrong and breaks stuff which does not require the broadcast > nonsense. > OK, sorry for not considering that case. > If TICK_ONESHOT is disabled, then everything is in periodic mode and > tick_broadcast_enter() rightfully returns 0. Ditto for 'highres=off' > on the command line. > > But there is a case which is not correctly handled right now. That's > what you are trying to solve in the wrong way. > Correct I was trying to solve exactly the case mentioned below. > If > GENERIC_CLOCKEVENTS_BROADCAST=n > > or > > GENERIC_CLOCKEVENTS_BROADCAST=y and no broadcast device is available, > > AND cpu local tick device has the C3STOP flag set, > > then we have no way to tell the idle code that going deep is not > allowed. > > So we need to be smarter than blindly changing a return > value. Completely untested patch below. > Agreed, thanks for the quick patch, I have tested it and it works fine. You can add Tested-by: Sudeep Holla Regards, Sudeep -- 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/