From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751912AbbGFPJg (ORCPT <rfc822;w@1wt.eu>);
	Mon, 6 Jul 2015 11:09:36 -0400
Received: from foss.arm.com ([217.140.101.70]:59939 "EHLO foss.arm.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750800AbbGFPJf (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 6 Jul 2015 11:09:35 -0400
Message-ID: <559A9A2B.2030705@arm.com>
Date: Mon, 06 Jul 2015 16:09:31 +0100
From: Sudeep Holla <sudeep.holla@arm.com>
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 <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>
CC: Sudeep Holla <sudeep.holla@arm.com>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Suzuki Poulose <Suzuki.Poulose@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Catalin Marinas <Catalin.Marinas@arm.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
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>
In-Reply-To: <20150705205221.724282507@linutronix.de>
Content-Type: text/plain; charset=iso-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Thomas,

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 <sudeep.holla@arm.com>

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. On connecting debugger, I found all the cpus are in
shallow idle state(i.e. WFI in ARM) but with interrupts disabled.

I am not really keen on the failing configuration. We have never tested
that before, though I found it working with CPUIdle disabled.

So please feel free to add:
Tested-by: Sudeep Holla <sudeep.holla@arm.com>

Regards,
Sudeep