From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755506AbbGFPo3 (ORCPT ); Mon, 6 Jul 2015 11:44:29 -0400 Received: from foss.arm.com ([217.140.101.70]:60134 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754404AbbGFPo0 (ORCPT ); Mon, 6 Jul 2015 11:44:26 -0400 Message-ID: <559AA256.5040305@arm.com> Date: Mon, 06 Jul 2015 16:44:22 +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 , 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 References: <20150705205032.103910828@linutronix.de> <20150705205221.724282507@linutronix.de> <559A9A2B.2030705@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 On 06/07/15 16:35, Thomas Gleixner wrote: > 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? > Correct. >> 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? > All CPUs have entered WFI with interrupts disabled and no way to wake them up. >> 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. > True. I just wanted to mention that this patch works for all the practical purposes. > 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. > Let me know if you want to test something to help debug this configuration. Regards, Sudeep