linux-kernel - Re: [PATCH] pps: Make pps_gen

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Message-ID: <1298064881.2431.3.camel@work-vm>
Date:	Fri, 18 Feb 2011 13:34:41 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alexander Gordeev <lasaine@....cs.msu.su>,
	Rodolfo Giometti <giometti@...ux.it>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] pps: Make pps_gen_parport depend on BROKEN

On Fri, 2011-02-18 at 22:16 +0100, Thomas Gleixner wrote:
> This driver causes hard lockups, when the active clock soure is
> jiffies. The reason is that it loops with interrupts disabled waiting
> for a timestamp to be reached by polling getnstimeofday(). Though with
> a jiffies clocksource, when that code runs on the same CPU which is
> responsible for updating jiffies, then we loop in circles for ever
> simply because the timer interrupt cannot update jiffies. So both UP
> and SMP can be affected.

Yuck.

Alexander, Rodolfo: Instead of polling on gtod, could you take a
timestamp, calculate the delay and then use udelay()?

thanks
-john


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