Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753162AbbHDQDe (ORCPT ); Tue, 4 Aug 2015 12:03:34 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:47931 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751801AbbHDQDc (ORCPT ); Tue, 4 Aug 2015 12:03:32 -0400 Message-ID: <55C0E24F.5020802@roeck-us.net> Date: Tue, 04 Aug 2015 09:03:27 -0700 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: =?windows-1252?Q?Uwe_Kleine-K=F6nig?= CC: linux-watchdog@vger.kernel.org, Wim Van Sebroeck , linux-kernel@vger.kernel.org, Timo Kokkonen , linux-doc@vger.kernel.org, Jonathan Corbet , kernel@pengutronix.de Subject: Re: [PATCH 2/8] watchdog: Introduce hardware maximum timeout in watchdog core References: <1438654414-29259-1-git-send-email-linux@roeck-us.net> <1438654414-29259-3-git-send-email-linux@roeck-us.net> <20150804121816.GM9999@pengutronix.de> <55C0DADF.9050505@roeck-us.net> <20150804155220.GV9999@pengutronix.de> In-Reply-To: <20150804155220.GV9999@pengutronix.de> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2849 Lines: 71 Hi Uwe, On 08/04/2015 08:52 AM, Uwe Kleine-K?nig wrote: > On Tue, Aug 04, 2015 at 08:31:43AM -0700, Guenter Roeck wrote: >> Hi Uwe, >> >> On 08/04/2015 05:18 AM, Uwe Kleine-K?nig wrote: >>> On Mon, Aug 03, 2015 at 07:13:28PM -0700, Guenter Roeck wrote: >>>> Introduce an optional hardware maximum timeout in the watchdog core. >>>> The hardware maximum timeout can be lower than the maximum timeout. >>> Is this only until all drivers are converted to make use of the central >>> worker? Otherwise this doesn't make sense, right? >>> >>>> Drivers can set the maximum hardare timeout value in the watchdog data >>> s/hardare/hardware/ >>> >> Always those fat fingers ;-) >> >>>> structure. If the configured timeout exceeds half the value of the >>>> maximum hardware timeout, the watchdog core enables a timer function >>>> to assist sending keepalive requests to the watchdog driver. >>> I don't understand why you want to halve the maximum hw-timeout. If my >>> watchdog has hw-max-timeout = 5s and userspace sets it to 3s there >>> should be no need for assistance?! I think the implementation is the >>> other way round? >>> >> It is supposed to reflect the _maximum_ timeout. That is different to >> the time between heartbeats, which is supposed to be less; using half >> the value of the maximum hardware timeout seemed to be a safe number. > Right, I got that. With hw-max-timeout = 5s the machine resets after 5s > not caring for the device. And so pinging repeatedly after 2.5s is fine. > But if userspace sets a timeout of 3s (probably with the intention to > ping with a frequency of 1/1.5s) there is no need for worker-assistance, > because the pings coming in each 1.5s provided by userspace are good > enough. > Yes, that is how it is supposed to work. >>>> +static inline bool watchdog_need_worker(struct watchdog_device *wdd) >>>> +{ >>>> + unsigned int hm = wdd->max_hw_timeout_ms; >>>> + unsigned int m = wdd->max_timeout * 1000; >>>> + >>>> + return watchdog_active(wdd) && hm && hm != m && >>>> + wdd->timeout * 500 > hm; >>> >>> I don't understand what max_timeout is now that there is max_hw_timeout. >>> So I don't understand why you need hm != m either. >>> >> >> Backward compatibility. A driver which does not set max_hw_timeout_ms, >> or sets both to the same value, by definition expects to handle everything >> internally, and thus no worker is configured. > And a driver that does > > max_timeout = 5 > max_hw_timeout = 5125 > > falls through the cracks. > Hmm - not that this configuration makes any sense, but you are right. I'll make it "hm < m". Thanks, Guenter -- 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/