From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753309AbaA3NoE (ORCPT ); Thu, 30 Jan 2014 08:44:04 -0500 Received: from mail-wg0-f47.google.com ([74.125.82.47]:52560 "EHLO mail-wg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752992AbaA3NoB (ORCPT ); Thu, 30 Jan 2014 08:44:01 -0500 Message-ID: <52EA5720.8010000@linaro.org> Date: Thu, 30 Jan 2014 14:44:00 +0100 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Nicolas Pitre , Preeti U Murthy CC: Olof Johansson , Russell King , Benjamin Herrenschmidt , Paul Mundt , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , "Rafael J. Wysocki" , linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 1/6] idle: move the cpuidle entry point to the generic idle loop References: <1391017513-12995-1-git-send-email-nicolas.pitre@linaro.org> <1391017513-12995-2-git-send-email-nicolas.pitre@linaro.org> <52E9C946.50704@linux.vnet.ibm.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/30/2014 06:28 AM, Nicolas Pitre wrote: > On Thu, 30 Jan 2014, Preeti U Murthy wrote: > >> Hi Nicolas, >> >> On 01/30/2014 02:01 AM, Nicolas Pitre wrote: >>> On Wed, 29 Jan 2014, Nicolas Pitre wrote: >>> >>>> In order to integrate cpuidle with the scheduler, we must have a better >>>> proximity in the core code with what cpuidle is doing and not delegate >>>> such interaction to arch code. >>>> >>>> Architectures implementing arch_cpu_idle() should simply enter >>>> a cheap idle mode in the absence of a proper cpuidle driver. >>>> >>>> Signed-off-by: Nicolas Pitre >>>> Acked-by: Daniel Lezcano >>> >>> As mentioned in my reply to Olof's comment on patch #5/6, here's a new >>> version of this patch adding the safety local_irq_enable() to the core >>> code. >>> >>> ----- >8 >>> >>> From: Nicolas Pitre >>> Subject: idle: move the cpuidle entry point to the generic idle loop >>> >>> In order to integrate cpuidle with the scheduler, we must have a better >>> proximity in the core code with what cpuidle is doing and not delegate >>> such interaction to arch code. >>> >>> Architectures implementing arch_cpu_idle() should simply enter >>> a cheap idle mode in the absence of a proper cpuidle driver. >>> >>> In both cases i.e. whether it is a cpuidle driver or the default >>> arch_cpu_idle(), the calling convention expects IRQs to be disabled >>> on entry and enabled on exit. There is a warning in place already but >>> let's add a forced IRQ enable here as well. This will allow for >>> removing the forced IRQ enable some implementations do locally and >> >> Why would this patch allow for removing the forced IRQ enable that are >> being done on some archs in arch_cpu_idle()? Isn't this patch expecting >> the default arch_cpu_idle() to have re-enabled the interrupts after >> exiting from the default idle state? Its supposed to only catch faulty >> cpuidle drivers that haven't enabled IRQs on exit from idle state but >> are expected to have done so, isn't it? > > Exact. However x86 currently does this: > > if (cpuidle_idle_call()) > x86_idle(); > else > local_irq_enable(); > > So whenever cpuidle_idle_call() is successful then IRQs are > unconditionally enabled whether or not the underlying cpuidle driver has > properly done it or not. And the reason is that some of the x86 cpuidle > do fail to enable IRQs before returning. > > So the idea is to get rid of this unconditional IRQ enabling and let the > core issue a warning instead (as well as enabling IRQs to allow the > system to run). But what I don't get with your comment is the local_irq_enable is done from the cpuidle common framework in 'cpuidle_enter_state' it is not done from the arch specific backend cpuidle driver. So the code above could be: if (cpuidle_idle_call()) x86_idle(); without the else section, this local_irq_enable is pointless. Or may be I missed something ? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog