linux-kernel - Re: RFC: [PATCH] clocksource: tcb: fix min

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Date:	Mon, 09 Sep 2013 10:18:02 +0200
From:	Ronald Wahl <ronald.wahl@...itan.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-kernel@...r.kernel.org, arm@...nel.org,
	John Stultz <john.stultz@...aro.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	Andres Salomon <dilinger@...ued.net>,
	Shawn Guo <shawn.guo@...aro.org>, linux-ar@...per.es
Subject: Re: RFC: [PATCH] clocksource: tcb: fix min_delta calculation

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 = 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?

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.

The now lost +1 has actually been added in 2007 to solve a rounding issue:

   http://permalink.gmane.org/gmane.linux.kernel/549744

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.

Opinions?

- ron

-- 
Ronald Wahl - ronald.wahl@...itan.com - Phone +49 375271349-0 Fax -99
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