linux-kernel - Re: [PATCH] Improve clocksource unstable warning

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Date:	Fri, 12 Nov 2010 15:52:39 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Andrew Lutomirski <luto@....edu>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	pc@...ibm.com
Subject: Re: [PATCH] Improve clocksource unstable warning

On Fri, 2010-11-12 at 18:48 -0500, Andrew Lutomirski wrote:
> On Fri, Nov 12, 2010 at 6:40 PM, john stultz <johnstul@...ibm.com> wrote:
> > On Fri, 2010-11-12 at 16:52 -0500, Andrew Lutomirski wrote:
> >
> >> if ( wd_elapsed < cs_elapsed and ( (cs_elapsed - wd_elapsed) %
> >> wd_wrapping_time ) < (something fairly small) )
> >>   bail;  // The watchdog most likely wrapped.
> >
> > Huh. The modulo bit may need tweaking as its not immediately clear its
> > right. Maybe the following is clearer?:
> >
> > if ((cs_elapsed > wd_wrapping_time)
> >        && (abs((cs_elapsed % wd_wrapping_time)-wd_elapsed) < MAX_DELTA)
> >        // should be ok.
> 
> I think this is wrong if wd_elapsed is large (which could happen if
> the real wd time is something like (2 * wd_wrapping_time -
> MAX_DELTA/4)).

But wd_elapsed can never be larger then wd_wrapping_time, right?

Or am I still missing something?

thanks
-john


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