Message-ID: <522DD386.2080003@pengutronix.de>
Date: Mon, 09 Sep 2013 15:56:22 +0200
From: Marc Kleine-Budde <mkl@pengutronix.de>
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To: Ronald Wahl <ronald.wahl@raritan.com>
CC: Thomas Gleixner <tglx@linutronix.de>,
        Nicolas Ferre <nicolas.ferre@atmel.com>, linux-kernel@vger.kernel.org,
        arm@kernel.org, John Stultz <john.stultz@linaro.org>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        Andres Salomon <dilinger@queued.net>, Shawn Guo <shawn.guo@linaro.org>,
        linux-ar@jasper.es
Subject: Re: RFC: [PATCH] clocksource: tcb: fix min_delta calculation
References: <517687AB.1040309@pengutronix.de> <1366722524-25991-1-git-send-email-mkl@pengutronix.de> <alpine.LFD.2.02.1304251618590.21884@ionos> <51794385.1030308@pengutronix.de> <51C31926.3060400@pengutronix.de> <522D843A.60401@raritan.com>
In-Reply-To: <522D843A.60401@raritan.com>
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On 09/09/2013 10:18 AM, Ronald Wahl wrote:
> On 20.06.2013 17:00, Marc Kleine-Budde wrote:
>> Hello Thomas,
>>
>> On 04/25/2013 04:53 PM, Marc Kleine-Budde wrote:
>>> On 04/25/2013 04:21 PM, Thomas Gleixner wrote:
>>>> On Tue, 23 Apr 2013, Marc Kleine-Budde wrote:
>>>>> The commit
>>>>>
>>>>>      77cc982 clocksource: use clockevents_config_and_register()
>>>>> where possible
>>>>>
>>>>> switches from manually calculating min_delta_ns (and others) and
>>>>> clockevents_register_device() to automatic calculation via
>>>>> clockevents_config_and_register(). During this conversation the "+
>>>>> 1" in
>>>>>
>>>>>      min_delta_ns =3D clockevent_delta2ns(1, &clkevt.clkevt) + 1;
>>>>>
>>>>> was lost. This leads to problems with schedule_delayed_work() with
>>>>> a delay of
>>>>> "1". Resulting in the work not scheduled in time.
>>>>
>>>> Errm. How is schedule_delayed_work() related to this?
>=20
> I also stumbled over this issue now after upgrading from 3.4.57 to
> 3.10.10. Even sleep() is unreliable - sleeping for 2 seconds often
> sleeps just more than 3 seconds.
>=20
> The now lost +1 has actually been added in 2007 to solve a rounding iss=
ue:
>=20
>   http://permalink.gmane.org/gmane.linux.kernel/549744
>=20
> So I think this should either be fixed by always rounding up in
> clockevent_delta2ns() or by adding +1 to the min_delta_ns in the
> clockevents_config_and_register() function. Dunno if rounding up will
> cause problems with the max_delta_ns as it might be too big then so
> probably the second approach is better.
>=20
> Opinions?

Thomas, any thoughts on this?

Marc
--=20
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


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