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

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Date:	Tue, 22 Feb 2011 19:20:52 +0300
From:	Alexander Gordeev <lasaine@....cs.msu.su>
To:	john stultz <johnstul@...ibm.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	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

Hi John,

В Fri, 18 Feb 2011 13:34:41 -0800
john stultz <johnstul@...ibm.com> пишет:

> 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()?

Sure, it's possible but it would be less precise IMHO. I'll test it.

-- 
  Alexander

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