From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754206AbbGFPfj (ORCPT ); Mon, 6 Jul 2015 11:35:39 -0400 Received: from www.linutronix.de ([62.245.132.108]:55804 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753392AbbGFPfd (ORCPT ); Mon, 6 Jul 2015 11:35:33 -0400 Date: Mon, 6 Jul 2015 17:35:26 +0200 (CEST) From: Thomas Gleixner To: Sudeep Holla cc: LKML , Ingo Molnar , Peter Zijlstra , Preeti U Murthy , Suzuki Poulose , Lorenzo Pieralisi , Catalin Marinas , "Rafael J. Wysocki" Subject: Re: [patch 1/2] tick/broadcast: Prevent deep idle states if no broadcast device available In-Reply-To: <559A9A2B.2030705@arm.com> Message-ID: References: <20150705205032.103910828@linutronix.de> <20150705205221.724282507@linutronix.de> <559A9A2B.2030705@arm.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 Jul 2015, Sudeep Holla wrote: > On 05/07/15 21:53, Thomas Gleixner wrote: > > If no broadcast device is installed and the cpu local timers stop in > > deeper idle states, then there is currently nothing telling the idle > > code that it should not go into deep idle states, so the timers stop > > and nothing wakes up the cpus. > > > > Make the broadcast_enter/exit() functions independent of the > > configuration options and always check on enter: > > > > - whether the cpu local device is affected by idle states > > - whether a broadcast device is available > > > > This covers all possible config combinations including > > CONFIG_BROADCAST=n. > > > > Reported-by: Sudeep Holla > > Sorry for the delay, took a while testing few configuration: > > +--------------+--------+--------------+--------------------+ > | Configs | PERIOD | HRTimers+NOHz|Cmdline(HR+NoHZ=off)| > +--------------+--------+--------------+--------------------+ > | UP w/o H/W BC| OK | OK | OK | > +--------------+--------+--------------+--------------------+ > | UP w/ H/W BC | OK | OK | OK | > +--------------+--------+--------------+--------------------+ > |SMP w/o H/W BC| OK* | OK | Not OK(**) | > +--------------+--------+--------------+--------------------+ > |SMP w/ H/W BC | OK | OK | OK | > +--------------+--------+--------------+--------------------+ > > H/W BC - Hardware Broadcast Timer source > > (*) None of the CPUs enters deeper idle states losing local timers > > (**)SMP build without Hardware Broadcast Timer source(i.e. one cpu is > the broadcast source) with HRTimers+NOHz configs but disabled in cmdline > fails to boot. That's using the hrtimer broadcast mechanism, right? > On connecting debugger, I found all the cpus are in > shallow idle state(i.e. WFI in ARM) but with interrupts disabled. And that means? > I am not really keen on the failing configuration. We have never tested > that before, though I found it working with CPUIdle disabled. Well, we should figure out what happens while we are at it before everything gets paged out again. In the case of CONFIG_NOHZ=n and CONFIG_HIGHRES=n the broadcast hrtimer is not compiled as it depends on CONFIG_TICK_ONESHOT, so it works via the bc.evtdev == NULL check. With either option enabled CONFIG_TICK_ONESHOT gets set, so the broadcast timer gets installed but somehow does not work proper if nohz and highres are disabled on the kernel command line. Thanks, tglx