linux-kernel - Re: [PATCH] hrtimer: increase clock min delta threshold while interrupt hanging

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Date:	Mon, 22 Dec 2008 10:05:45 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	Frans Pop <elendil@...net.nl>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hrtimer: increase clock min delta threshold while
	interrupt hanging


* Frédéric Weisbecker <fweisbec@...il.com> wrote:

> > Also, there's min_delta doubling in tick_dev_program_event() itself 
> > too - that interacts with the irq-overload logic:
> >
> > +       dev->min_delta_ns = (unsigned long)try_time.tv64 * 3;
> >
> >        Ingo
> 
> That's what I explained above, the doubling of min delta in 
> tick_dev_program_event() is never reached in my case. And moreover I'm 
> not sure it is ever reached whatever the call sites of 
> tick_dev_program_event() unless min delta has a very low value...

yeah, that looks all rather messy and probably ineffective. Thomas, mind 
to take a look?

Frederic's patch solves a real timer-irq-overload extreme situation so i 
find it rather valuable. Maybe we should do Frederic's patch as-is, have 
the 'softer' min_delta behavior for the usual hrtimer codepaths - and the 
more agressive one for the timer tick only?

	Ingo
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